Low resistance splice for high temperature superconductor wires

ABSTRACT

Under one aspect, a laminated, spliced superconductor wire includes a superconductor joint, which includes (i) first and second superconductor wires, each wire including a substrate, a superconductor layer overlying the substrate, and a cap layer overlying the superconductor layer; and (ii) a conductive bridge, the conductive bridge including a substrate, a superconductor layer overlying the substrate, and a cap layer overlying the superconductor layer, wherein the cap layer of the conductive bridge is in electrically conductive contact with a portion of the cap layer of each of the first and second superconductor wires through an electrically conductive bonding material. The spliced wire also includes (b) a stabilizer structure surrounding at least a portion of the superconductor joint, wherein the superconductor joint is in electrical contact with the stabilizer structure; and (c) a substantially nonporous electrically conductive filler, wherein the filler substantially surrounds the superconductor joint.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/832,724, the entire contents of which areincorporated herein in their entirety.

TECHNICAL FIELD

This application relates to the field of high temperaturesuperconductors.

BACKGROUND

High temperature superconductor (HTS) materials provide a means forcarrying extremely large amounts of current with extremely low loss. HTSmaterials lose all resistance to the flow of direct electrical currentand nearly all resistance to the flow of alternating current when cooledbelow a critical temperature. The development of HTS wires (theexpression “wires” is used here for a variety of conductors, includingtape-like conductors) using these materials promises a new generation ofhigh efficiency, compact, and environmentally friendly electricalequipment, which has the potential to revolutionize electric powergrids, transportation, materials processing, and other industries.However, a commercially viable product has stringent engineeringrequirements, which has complicated the implementation of the technologyin commercial applications.

In the second generation HTS wire (coated conductor) technology,currently under development, the HTS material is generally apolycrystalline rare-earth/alkaline-earth/copper oxide, e.g.yttrium-barium-copper oxide (YBCO). The current carrying capability ofthe HTS material is strongly related to its crystalline alignment ortexture. Grain boundaries formed by the misalignment of neighboringcrystalline superconductor grains are known to form an obstacle tosuperconducting current flow, but this obstacle decreases with theincreasing degree of alignment or texture. Therefore to make thematerial into a commercially viable product, e.g. an HTS wire, thesuperconducting material must maintain a high degree of crystallinealignment or texture over relatively long distances. Otherwise, thesuperconducting current carrying capacity (critical current density)will be limited.

A schematic of a typical second-generation HTS wire 100 is shown inFIG. 1. The wire includes substrate 110, buffer layer 120 (which couldinclude multiple buffer layers), superconductor layer 130, and cap layer140, and is fabricated as described below. It should be noted that inthis and all subsequent figures, the dimensions are not to scale.Superconductor materials can be fabricated with a high degree ofcrystallographic alignment or texture over large areas by growing a thinlayer 130 of the material epitaxially on top of a flexible tape-shapedsubstrate 110 and buffer layer 120, which are fabricated so that thesurface of the topmost layer has a high degree of crystallographictexture at its surface. When the crystalline superconductor material isgrown epitaxially on this surface, its crystal alignment grows to matchthe texture of the substrate. In other words, the substrate textureprovides a template for the epitaxial growth of the crystallinesuperconductor material. Further, the substrate provides structuralintegrity to the superconductor layer.

Substrate 110 and/or buffer 120 can be textured to provide a templatethat yields an epitaxial superconductor layer 130 with excellentsuperconducting properties such as high critical current density.Materials such as nickel, copper, silver, iron, silver alloys, nickelalloys, iron alloys, stainless steel alloys, and copper alloys can beused, among others, in the substrate. Substrate 110 can be texturedusing a deformation process, such as one involving rolling andrecrystallization annealing the substrate. An example of such a processis the rolling-assisted biaxially textured substrate (RABiTS) process.In this case large quantities of metal can be processed economically bydeformation processing and annealing and can achieve a high degree oftexture.

One or more buffer layers 120 can be deposited or grown on the surfaceof substrate 110 with suitable crystallographic template on which togrow the superconductor layer 130. Buffer layers 120 also can providethe additional benefit of preventing diffusion over time of atoms fromthe substrate 110 into the crystalline lattice of the superconductormaterial 130 or of oxygen into the substrate material. This diffusion,or “poisoning,” can disrupt the crystalline alignment and therebydegrade the electrical properties of the superconductor material. Bufferlayers 120 also can provide enhanced adhesion between the substrate 110and the superconductor layer 130. Moreover, the buffer layer(s) 120 canhave a coefficient of thermal expansion that is well matched to that ofthe superconductor material. For implementation of the technology incommercial applications, where the wire may be subjected to stress, thisfeature is desirable because it can help prevent delamination of thesuperconductor layer from the substrate.

Alternatively, a non-textured substrate 110 such as Hastelloy can beused, and textured buffer layer 120 deposited by means such as theion-beam-assisted deposition (IBAD) or inclined substrate deposition(ISD). Additional buffer layers 120 may be optionally depositedepitaxially on the IBAD or ISD layer to provide the final template forepitaxial deposition of an HTS layer 130.

By using a suitable combination of a substrate 110 and one or morebuffer layers 120 as a template, superconductor layer 130 can be grownepitaxially with excellent crystal alignment or texture, also havinggood adhesion to the template surface, and with a sufficient barrier topoisoning by atoms from the substrate. The superconductor layer 130 canbe deposited by any of a variety of methods, including the metal-organicdeposition (MOD) process, metal-organic chemical vapor deposition(MOCVD), pulsed laser deposition (PLD), thermal or e-beam evaporation,or other appropriate methods. Lastly, a cap layer 140 can be added tothe multilayer assembly, which helps prevent contamination of thesuperconductor layer from above. The cap layer 140 can be, e.g., silveror a silver-gold alloy, and can be deposited onto the superconductorlayer 130 by, e.g., sputtering. In the case where slitting is performedafter lamination, the cap layer may also include an additional laminatedmetal “stabilizer” layer, such as a copper or stainless steel layer,bonded to the cap layer, e.g., by soldering.

An exemplary as-fabricated multilayer HTS wire 100 includes a biaxiallytextured substrate 110 of nickel with 5% tungsten alloy; sequentiallydeposited epitaxial buffer layers 120 of Y₂O₃, YSZ, and CeO₂; epitaxiallayer 130 of YBCO; and a cap layer 140 of Ag. Exemplary thicknesses ofthese layers are: a substrate of about 25-75 microns, buffer layers ofabout 75 nm each, a YBCO layer of about 1 micron, and a cap layer ofabout 1-3 microns. HTS wires 100 as long as 100 m have been manufacturedthus far using techniques such as those described above.

During use, it is desirable that the HTS wire is able to tolerate bendstrains. A bend induces tensile strain on the convex outer surface ofthe bend, and compressive strain on the concave inner surface of thebend, thereby subjecting the HTS layer to tensile or compressive strainsdepending on the direction in which the wire is bent. While a modestamount of compressive stress can actually enhance the current carryingcapacity of an HTS layer, in general subjecting the whole assembly tostress (especially repeated stress) places the wire at risk ofmechanical damage. For example, cracks could be formed and propagate inthe HTS layer, degrading its mechanical and electrical properties, orthe different layers could delaminate from each other or from thesubstrate.

Methods for reducing stress in the HTS layer are described, e.g., inU.S. Pat. Nos. 6,745,059 and 6,828,507. For example, a copper strip,chosen to have similar thickness and mechanical features to thesubstrate, can be bonded onto the upper surface of the insert. Thissandwiches the HTS layer roughly in the middle of the overall structure,so if the assembly is bent, the HTS layer is neither at the outer norinner surface of the bend. Two of these assemblies can also be bondedtogether at their respective copper strips to form a single HTS wireassembly. In this case, the two substrates face outward, and the coppertapes are in the middle of the assembly. In this case the inclusion of asecond assembly provides additional current carrying capacity; however,electrical contact to the HTS layers requires splicing the wire open, orpartially removing one of the inserts in the contact section.

A further issue for coated conductor HTS wires is that of environmentalcontamination when the wire is in use. Environmental exposure can slowlydegrade the electrical performance of HTS layers. Also, in the presenceof cryogenic liquids such as liquid nitrogen in contact with the wire,the liquid can diffuse into pores within the wire, and on warming canform “balloons” that can damage the wire. Sealing the wire is desirableto prevent either environmental exposure of the HTS layers orpenetration of the liquid cryogen into the wire. Seals for HTSassemblies are described in, e.g. U.S. Pat. No. 6,444,917.

The coated conductor approach has been greatly advanced in recent yearsto the point where long length manufacturing of reinforced tapes isbeing established. However, the utility of these tapes would be greatlyincreased if they could be made to any required length via lowresistance joints that are mechanically robust and conform to tightgeometric tolerances.

SUMMARY

Low cost, low resistance, mechanically robust, and geometrically uniformjoints for superconductor wires are described.

Under one aspect, a laminated, spliced superconductor wire includes asuperconductor joint, which includes (i) first and second superconductorwires, each wire including a substrate, a superconductor layer overlyingthe substrate, and a cap layer overlying the superconductor layer; and(ii) a conductive bridge, the conductive bridge including a substrate, asuperconductor layer overlying the substrate, and a cap layer overlyingthe superconductor layer, wherein the cap layer of the conductive bridgeis in electrically conductive contact with a portion of the cap layer ofeach of the first and second superconductor wires through anelectrically conductive bonding material. The spliced wire also includes(b) a stabilizer structure surrounding at least a portion of thesuperconductor joint, wherein the superconductor joint is in electricalcontact with the stabilizer structure; and (c) a substantially nonporouselectrically conductive filler, wherein the filler substantiallysurrounds the superconductor joint.

One or more embodiments include one or more of the following features.The conductive bridge has a length selected to provide thesuperconductor joint with a predetermined conductivity. The conductivebridge is bonded to at least ten millimeters of the cap layers of eachof the first and second superconductor wires. The conductive bridge isbonded to at least ten centimeters of the cap layers of each of thefirst and second superconductor wires. The conductive bridge includes asection cut from one of the first and second superconductor wires. Thefiller bonds stabilizer structure to the superconductor joint. Theconductive filler includes a material selected from the group consistingof solder, metal, metal alloy, metal amalgam, and conductive polymer.The conductive filler and the conductive bonding material have the samecomposition. The conductive filler and the conductive bonding materialhave melting points that differ by less than about 10%. The electricallyconductive bonding material includes low resistance solder. The lowresistance solder includes one of indium, Pb—Sn, and Pb—Sn—Ag. The lowresistance solder forms edge seals on an end of each of the first andsecond superconductor wires and on first and second ends of theconductive bridge. An end of at least one of the first and secondsuperconductive wires and the conductive bridge is cut so as to mitigatestress in the spliced wire. The end is cut on a diagonal. Insulationsurrounding at least the superconductor joint. The first and secondsuperconductor wires and the conductive bridge each further include abuffer layer between the substrate and the superconductor layer. The caplayer of the first and second superconductor wires and the conductivebridge include silver. The stabilizer structure includes a metalselected from the group consisting of aluminum, copper, silver, nickel,iron, stainless steel, aluminum alloy, copper alloy, silver alloy,nickel alloy, and iron alloy. A conductive pathway between the first andsecond wires has a resistance of less than about 1 milli-ohm. Aconductive pathway between the first and second wires has a resistanceof less than about 500 micro-ohms. A conductive pathway between thefirst and second wires has a resistance of less than about 200milli-ohms. A conductive pathway between the first and second wires hasa resistance of less than about 100 milli-ohms.

Under another aspect, a laminated, spliced superconductor wire includes(a) first and second stabilized superconductor wires, each wireincluding a substrate, a superconductor layer overlying the substrate, acap layer overlying the superconductor layer, and a stabilizer structurebonded with electrically conductive filler to the cap layer. Thelaminated, spliced superconductor wire also includes (b) a conductivebridge, the conductive bridge including a substrate, a superconductorlayer overlying the substrate, a cap layer overlying the superconductorlayer, and a stabilizer structure bonded with electrically conductivefiller to the cap layer, wherein the conductive bridge is inelectrically conductive contact with a portion of each of the first andsecond superconductor wires through an electrically conductive bondingmaterial. The laminated, spliced superconductor wire also includes (c) aplurality of edge seals, a first edge seal substantially sealing an endof the first wire, a second edge seal substantially sealing an end ofthe second wire, and third and fourth edge seals respectivelysubstantially sealing first and second ends of the conductive bridge.

One or more embodiments include one or more of the following features.The stabilizer structures of each of the first wire, second wire, andconductive bridge are thinned in regions where the conductive bridge isin electrically conductive contact with the first and second wires. Thestabilizer structures of each of the first wire, second wire, andconductive bridge are removed in regions where the conductive bridge isin electrically conductive contact with the first and second wires. Theconductive bridge is in electrically conductive contact with at leastten millimeters of each of the first and second superconductor wires.The conductive bridge is in electrically conductive contact with atleast ten centimeters of each of the first and second superconductorwires. The conductive filler and the conductive bonding material havemelting points that differ by less than about 10%. The electricallyconductive bonding material and the conductive filler each include lowresistance solder. The low resistance solder includes one of indium,Pb—Sn, and Pb—Sn—Ag. A conductive pathway between the first and secondwires has a resistance of less than about 1 milli-ohm. A conductivepathway between the first and second wires has a resistance of less thanabout 500 micro-ohms. A conductive pathway between the first and secondwires has a resistance of less than about 200 milli-ohms. A conductivepathway between the first and second wires has a resistance of less thanabout 100 milli-ohms. The spliced wire of claim 23, wherein thestabilizer structure comprises first and second stabilizer strips.

The expression “HTS wire” or “HTS tape” is intended to indicate amultilayer structure for use in carrying current. The wire or tape maybe substantially sealed to the environment. An HTS wire or tapetypically includes a substrate, one or more buffer layers, asuperconductor layer, a cap layer, and optionally a stabilizer layerthat can be considered part of the cap layer. Generally in this HTS wireor tape, the superconductor layer can be electrically isolated from themetallic substrate by the buffer layer(s). However, if electricallyconductive buffer layers are used, the superconductor layer can beelectrically connected to the metal substrate. Alternatively, anelectrically conductive cap layer can be in contact with both thesuperconductor layer and the substrate, and provide electrical contactbetween the two.

The expression “sealed” is intended to mean substantially surrounded andsubstantially physically isolated from the environment. The expression“sealed” may include, but is not required to include, substantialimpermeability to penetration from gas or liquid under normalcircumstances.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 is a cross-sectional view of a typical HTS wire.

FIG. 2A is a cross-sectional side view of a first HTS wire spliced to asecond HTS wire by a conductive bridge according to one or moreembodiments of the invention.

FIG. 2B is a cross-sectional view along line 1-1 of the embodimentillustrated in FIG. 2A.

FIG. 2C is a cross-sectional side view of a first HTS wire spliced to asecond HTS wire by a conductive bridge according to one or moreembodiments of the invention.

FIG. 2D is a cross-sectional view along line 2-2 of the embodimentillustrated in FIG. 2C.

FIG. 2E is a cross-sectional side view of a first HTS wire spliced to asecond HTS wire by a conductive bridge according to one or moreembodiments of the invention.

FIG. 2F is a cross-sectional view along line 3-3 of the embodimentillustrated in FIG. 2E.

FIG. 3A is a flow chart of a method for fabricating two HTS wires andsplicing them together with a conductive bridge according to one or moreembodiments of the invention.

FIG. 3B is a flow chart of a method for fabricating two HTS wires andsplicing them together with a conductive bridge according to one or moreembodiments of the invention.

FIG. 3C is a schematic illustration of a system and process used tolaminate HTS wires to stabilizer strips according to one or moreembodiments of the invention.

FIG. 4 is a schematic illustration of a system and process used toprepare a spliced HTS wire according to one or more embodiments of theinvention.

FIG. 5 is a plot of overlap length versus resistance for several examplespliced HTS wires.

FIG. 6 is a plot of the double bend properties of several examplespliced HTS wires.

FIG. 7 is a plot of the splice wind tolerance Ic retention of severalexample spliced HTS wires.

FIG. 8 is a plot of the splice wind tolerance Ic retention of severalexample spliced HTS wires.

FIG. 9 is a plot of the splice wind tolerance Ic retention of severalexample spliced HTS wires.

FIG. 10 is a plot of the double bend properties of several examplespliced HTS wires.

FIG. 11 is a plot of the double bend properties of several examplespliced HTS wires.

FIG. 12 is a plot of the double bend properties of several examplespliced HTS wires.

FIG. 13 is a micrograph of an exemplary spliced HTS wire.

FIG. 14 is a micrograph of an exemplary spliced HTS wire.

DETAILED DESCRIPTION

High temperature superconductor (HTS) wires are spliced together atjoints to form wires that are arbitrarily long. Each joint between twoHTS wires includes a conductive bridge that is laminated to both wires.The conductive bridge provides a low-resistance electrical pathwaybetween the two wires, and also provides mechanical stability so thatthe joint can be flexed or bent without breaking the electricalconnection between the wires and without damaging the HTS layers of thewires.

FIG. 2 illustrates a low-resistance joint 200 between two HTS wires 210,220. Joint 200 includes first HTS wire 210, second HTS wire 220, andconductive bridge 230. Low resistance solder 240 bonds one end ofconductive bridge 230 to one end of first HTS wire 210, and bonds theother end of conductive bridge 230 to one end of second HTS wire 220.The joint also includes edge seals 250 of low resistance solder at theend of each HTS wire or conductive bridge. Note that only one end ofeach of first HTS wire 210 and second HTS wire 220 is shown, because thewires are long compared to the length of joint 200.

In operation, current flows from first HTS wire 210, through solder 240and into conductive bridge 230, then flows through solder 240 and intosecond HTS wire 220. This kind of joint is particularly useful forasymmetrical HTS wires, where one side of the wire has a much lowerelectrical resistance than the other side. Joining two such wires with aconductive bridge, e.g., as illustrated in FIGS. 2A-2D, allows currentto flow through the low resistance sides of each of the two wires 210,220 and conductive bridge 230, and also maintains the overall symmetryof the wire, so that the substrate will generally remain on the sameside of the wire on both sides of the joint. In contrast, a simple lapjoint between two wires would result in the substrate being on oppositesides of the wire on either side of the joint, and a butt joint betweentwo wires would exhibit high resistivity as well as low mechanicalstability.

First HTS wire 210, second HTS wire 220, and conductive bridge 230 mayall be the same kind of HTS wire, e.g., the wire illustrated in FIG. 1.Here, first and second HTS wires 210, 220 both have their respective caplayers 260, 261 facing up, and conductive bridge 230 is flipped over sothat its cap layer 262 faces down, i.e., facing the cap layer of the twowires 210, 220. The cap layers 260, 261, and 262 are each conductive,i.e., have a relatively low electrical resistance, and are relativelythin. Thus, arranging two cap layers to electrically contact each other,e.g., placing them adjacent to each other and bonded together with lowresistance solder 240, provides a low electrical resistance pathwaybetween two HTS wires. In contrast, the substrate has a relatively highelectrical resistance, and may even be insulative, so a joint formed bycontacting the substrate sides of wires 210, 220 and conductive strap230 wire would be unsatisfactorily resistive.

The joint itself may be relatively long, providing a long electricalpathway, i.e., a large contact area, over which to transfer current fromthe first HTS wire 210 into conductive bridge 230 and then fromconductive bridge 230 into second HTS wire 220, and thus reducing theresistance of the joint. For example, conductive bridge 230 may range inlength from several centimeters to many meters, and its overlap witheach HTS wire may range in length from several millimeters up to severalmeters. This way, although a joint may not be as conductive as a singleHTS wire, the electrical resistance of the joint may be made low enoughto allow the spliced wire to carry a normal operating current.

As mentioned above, a low resistance solder 240 such as indium, Pb—Sn,or Pb—Sn—Ag provides the bonding between cap layers 260, 261, and 262.Wetting of the solder 240 may be enhanced with chemical flux that isapplied in situ or prior to melting, by mechanical abrasion inducedsurface activation, or by surface treatments such as plasma etching. Thefour transition regions from overlap to single wire can optionally betreated by forming solder edge seals 250 from the top of the ledge atthe end of the wire down to and along the wire, extending from the cutend. This substantially seals the end to the environment, and alsoreduces the stress and strain that the wire experiences because of thesharp ledge, which in some circumstances could otherwise lead tokinking, delamination, and/or degradation of the superconductor layerand its critical current. The ends of wires 210 and 220 and conductivebridge 230 may also be cut so as to mitigate the formation of a burr orother protrusion. For example, the ends may be cut on an angle such as adiagonal, so as to reduce the presence of sharp corners in the joint.However, as discussed in greater detail below, the use of certainmaterials and architectures reduces mechanical stress in the joint, thusobviating the need for cutting the wire ends, or providing solder edgeseals, in some applications.

FIG. 2B shows a cross-section of joint 200 along line 1-1. The cap layer262 of conductive bridge 230 is bonded to the cap layer 261 of wire 220with solder 240.

In other embodiments, substantially sealing the joined wire to theenvironment can inhibit and/or prevent contamination of the HTS layer.FIG. 2C illustrates one embodiment of a substantially sealedlow-resistance joint 200′. As in FIG. 2A, joint 200′ includes first HTSwire 210′, second HTS wire 220′, and conductive bridge 230′. Lowresistance solder 240′ bonds one end of conductive bridge 230′ to oneend of first HTS wire 210′, and bonds the other end of conductive bridge230′ to one end of second HTS wire 220′. The joint also includes edgeseals 250′ of low resistance solder at the end of each HTS wire orconductive bridge. The embodiment illustrated in FIG. 2B also includes apair of stabilizer strips on either side of the joint, which are bondedto assembly 210′, 220′, 230′ with filler 280′. Filler 280′ substantiallysurrounds and seals the assembly 210′, 220′, 230′ to the environment,and is substantially non-porous. In some embodiments filler 280′ may bea conductive material such as solder, e.g., Pb—Sn or Pb—Sn—Ag solder.

Note however that solder “ramps” such as illustrated in FIG. 2C need notbe included in all embodiments. For example, the ends of wires 210′,220′ and conductive bridge 230′ can instead be sealed with solder beadsof arbitrary shape. Or, for example, the ends of wires 210′, 220′ andconductive bridge 230′ need not be sealed using edge seals 250′ at all,but rather the presence of filler 280′ can be used to seal the ends. Anadditional material can also be used to enhance adhesion of the filler280′ to the ends of wires 210′, 220′ and conductive bridge 230′.

FIG. 2D is a view along line 2-2 of the embodiment illustrated in FIG.2C. The cap layer 262′ of conductive bridge 230′ is bonded to the caplayer 261′ of wire 220′ with solder 240′. Additionally, filler 280′substantially surrounds assembly 220′, 230′, and bonds assembly 220′,230′ to stabilizer strips 270′ and 271′.

FIG. 2E illustrates an embodiment of a joint 200″ that includes wiresthat are each stabilized with stabilizer strips. Here, each of wires210″, 220″ and conductive bridge 230″ includes wire 100″ which may besubstantially the same as the wires described above, e.g., including asubstrate, buffer layer(s), an HTS layer, and a cap layer 262″. Each ofwires 210″, 220″, and conductive bridge 230″ also include filler 280″which bonds the respective wire or bridge to upper and lower stabilizerstrips. The wires 210″, 220″ are then joined to the conductive bridgeusing solder 240″ which also forms edge seals 250″. The upper stabilizerstrip 272″ of wire 210″ is bonded to the lower stabilizer strip 271″ ofconductive bridge 230″ such that the HTS layers are positionedrelatively closely, e.g., separated from each other by stabilizer strips271″, 272″, filler 280″, solder 240″, and the respective cap layers ofthe wire and bridge, but not separated by a substrate. Thus theconductive pathway between the HTS layers includes relatively highlyconductive materials, thus reducing the overall pathway resistance. Theupper stabilizer strip 273″ of wire 210″ is similarly bonded to thelower stabilizer strip 271″ of conductive bridge 230″.

FIG. 2F is a view along line 3-3 of the embodiment illustrated in FIG.2E. The lower stabilizer strip 271″ of conductive bridge 230″ is bondedto the upper stabilizer strip 273″ of wire 220″ with solder 240″.Additionally, within conductive bridge 230″, filler 280″ substantiallysurrounds the substrate/buffer/HTS/cap layer assembly, and bonds thatassembly to stabilizer strips 270″ and 271″. Within wire 220″, thefiller similarly substantially surrounds the substrate/buffer/HTS/caplayer assembly and bonds that assembly to stabilizer strips 273″ and274″.

Optionally, the stabilizer strip on one side of each of the wires may beremoved or reduced in thickness from the intended overlap region of eachend, by for example etching, mechanical abrasion or melt—peeling.Removing or reducing the thickness of the stabilizer strip reduces thejoint resistance, because the stabilizer strip may have a somewhathigher resistivity than is desirable over the length of the joint.Alternatively, the stabilizer strip may be left in the wire, and theoverlap joint may be lengthened within practical limits to compensatefor the additional through joint resistance the stabilizer strip causes.If a higher resistance joint is desired (fault current limiter wire), alayer of stainless steel or other high resistance metal in between thesplice can be used to raise the overall resistance of the splice. Also,for example, electrical-insulation coated and/or sealed HTS wires can bejoined using the methods described herein. Here, the insulation isremoved from the overlap region before or during the splicing operation.Insulation may also be applied or re-applied after the conductive bridgesplice joint is made to electrically insulate and/or to seal theconductive bridge splice region.

In the embodiments illustrated in FIGS. 2B and 2C, the back side of thesubstrates (the side opposite the buffer/HTS/cap layers) can be treatedto enhance wetting of the substrate by filler 280′. For example, asdescribed in U.S. patent application Ser. No. 11/193,262, filed Jul. 19,2005 and entitled “Architecture for High Temperature SuperconductorWire,” the entire contents of which are incorporated by reference, someuseful wetting layers include Ag, Cu, Ni, Ti, and TiN, which can becoated onto the substrate using, e.g., sputtering.

In embodiments in which current flows through stabilizer strips as itpasses through the joint, the surface of the stabilizer strip can bemodified prior to lamination in order to improve the resistivity of thejoint and/or adhesion of filler or solder to the stabilizer strip. Forexample, for copper stabilizer strips, a layer of low melting pointmetal, such as solder or Sn, can be applied to the strips in order toenable faster bonding. Or, for example, for stainless steel stabilizerstrips, a Nickel strike layer and a layer pure Sn can be applied,although other low melting point alloys could be used. The Ni strikelayer is used to improve the adhesion of Sn to the stainless steel. TheSn layer improves the wettability of the stainless steel by the solderduring later lamination to the superconductor wire. The thickness of theSn layer can range, e.g., from 40 micro inches to 200 or more microinches, e.g., 50 micro inches. Before application of the Ni and Snlayers, the stainless steel stabilizer strips are prepared byelectrically, chemically or mechanically cleaning the surface, e.g., byusing a fully activated stainless steel flux, or by scrubbing thesurface with an abrasive wheel. This preparation activates the stainlesssteel, eliminating Cr₂O₃ oxide from the surface and thus reducing theresistivity of the surface. Or, for example, for brass stabilizerstrips, such stringent activation is not necessary. The brass can becleaned with a mild detergent and plated with Sn, Sn—Pb, or Cu, forexample.

In different embodiments, different materials are suitable for use asfiller and/or solder in the joint and/or wires. For example, althoughmany of the example wires described below use indium solder, Sn—Pb andSn—Pb—Ag may also be suitable. Depending on the filler used to laminatestabilizer strips to the assembly, Sn—Pb and Sn—Pb—Ag may have a similarmelting point and a similar mechanical strength to the filler, and thusreduce thermal and mechanical mismatch between the solder and the fillerwhich can result in delamination upon stress. For example, in the casewhere both the filler and the solder used is Sn—Pb, the mismatch wouldbe negligible and thus result in a particularly strong joint. Thus insome embodiments, solder “ramps” need not have the same configuration asthat shown in FIG. 2A in order to mitigate kinking, delamination, and/ordegradation of the superconductor layer.

Other architectures for stabilizing joined wires can also be used. Someexemplary architectures that can be used to stabilize joined wires aredescribed in U.S. patent application Ser. No. 11/193,262.

FIG. 3A illustrates an exemplary method for producing the joined HTSwires illustrated in FIGS. 2A-2D. First, the first HTS wire isfabricated. A substrate is provided (310); a buffer layer is depositedon the substrate (320); a superconductor layer is deposited on thebuffer layer (330); and a cap layer is deposited over the superconductorlayer (340). Separately, the second HTS wire is fabricated by providinga substrate (310′); depositing a buffer layer on the substrate (320′);depositing a superconductor layer on the buffer layer (330′); anddepositing a cap layer over the superconductor layer (340′).

Next, a conductive bridge is cut from the first wire (350). In otherembodiments, the conductive bridge is provided from a third HTS wire.The length of the conductive bridge is selected to provide asatisfactory electrical resistance over the entire length of the joint.As mentioned above, the end of the conductive bridge and/or the firstwire may be cut so as to mitigate the formation of burrs, as well as toreduce stress in the joint, e.g., by cutting the ends on a diagonal.Next, the cap layer at the first end of the conductive bridge is bondedto the cap layer at the end of the first wire (360). This is done bywetting the first end of the conductive bridge with solder, wetting theend of the first wire with solder, and pressing the two together, e.g.,in a die. Next, the cap layer at the second end of the conductive bridgeis similarly bonded to the cap layer at the end of the second wire(370). The solder is then optionally re-flowed to form edge seals suchas those illustrated in FIGS. 2A and 2C (380). Next, the resultingassembly is optionally laminated to stabilizer strips, forming asubstantially sealed and mechanically stabilized wire such as thatillustrated in FIGS. 2C-2D. Lateral and through-tape alignment of theoverlap at each of tape end is maintained during splice soldering andre-flow by edge guides or channels, as well as a sled or pressure bar orfixture for the top and bottom surfaces. The conductive bridge tape andthe two end regions of the spliced tape are aligned in the lateraldirection through the joint to within about 2 degrees of divergence fromthe conductive bridge axis line.

If the first and/or second HTS wires and/or conductive bridge arereinforced with a stabilizer strip laminated to the cap layer, thesplice and re-flow temperatures are kept below the incipient meltingtemperature of the material that laminates the stabilizer strip to thecap layer, e.g., solder or its related phases formed from solderinteraction with the cap layer and the stabilizer strip.

If desired, or sealing material such as an electrically insulatingcoating, can be applied to one or both sides of the spliced wire, orcompletely surrounding the spliced wire.

FIG. 3B illustrates an exemplary method for producing the joined HTSwire illustrated in FIGS. 2E-2F. First, the first HTS wire isfabricated. A substrate is provided (311); a buffer layer is depositedon the substrate (321); a superconductor layer is deposited on thebuffer layer (331); a cap layer is deposited over the superconductorlayer (341), and the resulting assembly is laminated to stabilizerstrips (391). Separately, the second HTS wire is fabricated by providinga substrate (311′); depositing a buffer layer on the substrate (321′);depositing a superconductor layer on the buffer layer (331′); depositinga cap layer over the superconductor layer (340′), and the resultingassembly is laminated to stabilizer strips (391′).

Next, a conductive bridge is cut from the first wire (351). In otherembodiments, the conductive bridge is provided from a third HTS wire.The length of the conductive bridge is selected to provide asatisfactory electrical resistance over the entire length of the joint.As mentioned above, the end of the conductive bridge and/or the firstwire may be cut so as to mitigate the formation of burrs, as well as toreduce stress in the joint, e.g., by cutting the ends on a diagonal.Next, the stabilizer strip at the first end of the conductive bridge isbonded to the stabilizer strip at the end of the first wire (361). Thisis done by wetting the first end of the conductive bridge with solder,wetting the end of the first wire with solder, and pressing the twotogether, e.g., in a die. Next, the stabilizer strip at the second endof the conductive bridge is similarly bonded to the stabilizer strip atthe end of the second wire (371). The solder is then optionallyre-flowed to form edge seals such as those illustrated in FIGS. 2E and2F (381). As mentioned above, lateral and through-tape alignment of theoverlap at each of tape end is maintained during splice soldering andre-flow by edge guides or channels, as well as a sled or pressure bar orfixture for the top and bottom surfaces. The conductive bridge tape andthe two end regions of the spliced tape are aligned in the lateraldirection through the joint to within about 2 degrees of divergence fromthe conductive bridge axis line.

In general, the steps of the method can be executed in a different orderthan that given. For example, the conductive bridge could besimultaneously bonded to both wires. Or, the conductive bridge could becut from the second wire, or could come from a separate wire, whichcould be different from either of the first or second HTS wires. Thesteps of the method can be performed manually and/or automatically. Forexample, cutting the ends of the wires can be performed manually, andpressing the solder-wetted conductive bridge and wire(s) together can beperformed automatically, e.g., in a die. Note also that the joint neednot solely be used to join two separately fabricated wires; the joint isalso useful for repairing a break in a single wire, or generally forproviding a low-resistance electrical connection between any two coatedconductor HTS wires.

A method for making an YBCO HTS wire that can be joined using themethods described herein is described. Other kinds of HTS wires can bejoined using the methods described herein, and the conductive bridge,first wire, and second wire need not be identical. For example the HTSwire can be a bismuth-strontium-calcium copper oxide (BSCCO)superconductor or a MgB superconductor.

Fabricating and Splicing HTS Wires

A web coating method of fabricating wires having the architectureCeO₂/YSZ/Y₂O₃/NiW is shown in FIG. 4.

Textured Metal Substrate

The template is provided in widths of about 1 to 10 cm, or larger.Optionally, it is textured. A method of preparing a textured metalsubstrate suitable for use as a substrate for an HTS wire first isdescribed. At a first station 410, a substrate is treated to obtainbiaxial texture. Preferably, the substrate surface has a relativelywell-defined crystallographic orientation. For example, the surface canbe a biaxially textured surface (e.g., a (113)[211] surface) or a cubetextured surface (e.g., a (100)[011] surface or a (100)[001] surface).Preferably, the peaks in an X-ray diffraction pole figure of surface 110have a FWHM of less than about 20° (e.g., less than about 15°, less thanabout 10°, or from about 5° to about 10°).

The surface of the substrate can be prepared, for example, by rollingand annealing. Surfaces can also be prepared using vacuum processes,such as ion beam assisted deposition, inclined substrate deposition andother vacuum techniques known in the art to form a biaxially texturedsurface on, for example, a randomly oriented polycrystalline surface. Incertain embodiments (e.g., when ion beam assisted deposition is used),the surface of the substrate need not be textured (e.g., the surface canbe randomly oriented polycrystalline, or the surface can be amorphous).

The substrate can be formed of any material capable of supporting abuffer layer stack and/or a layer of superconductor material. Examplesof substrate materials that can be used as the substrate include forexample, metals and/or alloys, such as nickel, silver, copper, zinc,aluminum, iron, chromium, vanadium, palladium, molybdenum and/or theiralloys. In some embodiments, the substrate can be formed of asuperalloy. In certain embodiments, the substrate can be in the form ofan object having a relatively large surface area (e.g., a tape or awafer). In these embodiments, the substrate is preferably formed of arelatively flexible material.

In some of these embodiments, the substrate is a binary alloy thatcontains two of the following metals: copper, nickel, chromium,vanadium, aluminum, silver, iron, palladium, molybdenum, tungsten, goldand zinc. For example, a binary alloy can be formed of nickel andchromium (e.g., nickel and at most 20 atomic percent chromium, nickeland from about five to about 18 atomic percent chromium, or nickel andfrom about 10 to about 15 atomic percent chromium). As another example,a binary alloy can be formed of nickel and copper (e.g., copper and fromabout five to about 45 atomic percent nickel, copper and from about 10to about 40 atomic percent nickel, or copper and from about 25 to about35 atomic percent nickel). As a further example, a binary alloy cancontain nickel and tungsten (e.g., from about one atomic percenttungsten to about 20 atomic percent tungsten, from about two atomicpercent tungsten to about 10 atomic percent tungsten, from about threeatomic percent tungsten to about seven atomic percent tungsten, aboutfive atomic percent tungsten). A binary alloy can further includerelatively small amounts of impurities (e.g., less than about 0.1 atomicpercent of impurities, less than about 0.01 atomic percent ofimpurities, or less than about 0.005 atomic percent of impurities).

In certain of these embodiments, the substrate contains more than twometals (e.g., a ternary alloy or a quaternary alloy). In some of theseembodiments, the alloy can contain one or more oxide formers (e.g., Mg,Al, Ti, Cr, Ga, Ge, Zr, Hf, Y, Si, Pr, Eu, Gd, Th, Dy, Ho, Lu, Th, Er,Tm, Be, Ce, Nd, Sm, Yb and/or La, with Al being the preferred oxideformer), as well as two of the following metals: copper, nickel,chromium, vanadium, aluminum, silver, iron, palladium, molybdenum, goldand zinc. In certain of these embodiments, the alloy can contain two ofthe following metals: copper, nickel, chromium, vanadium, aluminum,silver, iron, palladium, molybdenum, gold and zinc, and can besubstantially devoid of any of the aforementioned oxide formers.

In embodiments in which the alloys contain an oxide former, the alloyscan contain at least about 0.5 atomic percent oxide former (e.g., atleast about one atomic percent oxide former, or at least about twoatomic percent oxide former) and at most about 25 atomic percent oxideformer (e.g., at most about 10 atomic percent oxide former, or at mostabout four atomic percent oxide former). For example, the alloy caninclude an oxide former (e.g., at least about 0.5 aluminum), from about25 atomic percent to about 55 atomic percent nickel (e.g., from about 35atomic percent to about 55 atomic percent nickel, or from about 40atomic percent to about 55 atomic percent nickel) with the balance beingcopper. As another example, the alloy can include an oxide former (e.g.,at least about 0.5 atomic aluminum), from about five atomic percent toabout 20 atomic percent chromium (e.g., from about 10 atomic percent toabout 18 atomic percent chromium, or from about 10 atomic percent toabout 15 atomic percent chromium) with the balance being nickel. Thealloys can include relatively small amounts of additional metals (e.g.,less than about 0.1 atomic percent of additional metals, less than about0.01 atomic percent of additional metals, or less than about 0.005atomic percent of additional metals).

A substrate formed of an alloy can be produced by, for example,combining the constituents in powder form, melting and cooling or, forexample, by diffusing the powder constituents together in solid state.The alloy can then be formed by deformation texturing (e.g., annealingand rolling, swaging, extrusion and/or drawing) to form a texturedsurface (e.g., biaxially textured or cube textured). Alternatively, thealloy constituents can be stacked in a jelly roll configuration, andthen deformation textured. In some embodiments, a material with arelatively low coefficient of thermal expansion (e.g., Nb, Mo, Ta, V,Cr, Zr, Pd, Sb, NbTi, an intermetallic such as NiAl or Ni₃Al, ormixtures thereof) can be formed into a rod and embedded into the alloyprior to deformation texturing.

In some embodiments, stable oxide formation at the surface can bemitigated until a first epitaxial (for example, buffer) layer is formedon the biaxially textured alloy surface, using an intermediate layerdisposed on the surface of the substrate. Intermediate layers includethose epitaxial metal or alloy layers that do not form surface oxideswhen exposed to conditions as established by PO₂ and temperaturerequired for the initial growth of epitaxial buffer layer films. Inaddition, the buffer layer acts as a barrier to prevent substrateelement(s) from migrating to the surface of the intermediate layer andforming oxides during the initial growth of the epitaxial layer. Absentsuch an intermediate layer, one or more elements in the substrate wouldbe expected to form thermodynamically stable oxide(s) at the substratesurface which could significantly impede the deposition of epitaxiallayers due to, for example, lack of texture in this oxide layer.

In some of these embodiments, the intermediate layer is transient innature. “Transient,” as used herein, refers to an intermediate layerthat is wholly or partly incorporated into or with the biaxiallytextured substrate following the initial nucleation and growth of theepitaxial film. Even under these circumstances, the intermediate layerand biaxially textured substrate remain distinct until the epitaxialnature of the deposited film has been established. The use of transientintermediate layers may be preferred when the intermediate layerpossesses some undesirable property, for example, the intermediate layeris magnetic, such as nickel.

Exemplary intermediate metal layers include nickel, gold, silver,palladium, and alloys thereof. Additional metals or alloys may includealloys of nickel and/or copper. Epitaxial films or layers deposited onan intermediate layer can include metal oxides, chalcogenides, halides,and nitrides. In some embodiments, the intermediate metal layer does notoxidize under epitaxial film deposition conditions.

Care should be taken that the deposited intermediate layer is notcompletely incorporated into or does not completely diffuse into thesubstrate before nucleation and growth of the initial buffer layerstructure causes the epitaxial layer to be established. This means thatafter selecting the metal (or alloy) for proper attributes such asdiffusion constant in the substrate alloy, thermodynamic stabilityagainst oxidation under practical epitaxial buffer layer growthconditions and lattice matching with the epitaxial layer, the thicknessof the deposited metal layer has to be adapted to the epitaxial layerdeposition conditions, in particular to temperature.

Deposition of the intermediate metal layer can be done in a vacuumprocess such as evaporation or sputtering, or by electro-chemical meanssuch as electroplating (with or without electrodes). These depositedintermediate metal layers may or may not be epitaxial after deposition(depending on substrate temperature during deposition), but epitaxialorientation can subsequently be obtained during a post-deposition heattreatment.

In certain embodiments, sulfur can be formed on the surface of thesubstrate in a surface treatment. The sulfur can be formed on thesurface of the substrate, for example, by exposing the intermediatelayer to a gas environment containing a source of sulfur (e.g., H₂S) andhydrogen (e.g., hydrogen, or a mix of hydrogen and an inert gas, such asa 5% hydrogen/argon gas mixture) for a period of time (e.g., from about10 seconds to about one hour, from about one minute to about 30 minutes,from about five minutes to about 15 minutes). This can be performed atelevated temperature (e.g., at a temperature of from about 450° C. toabout 1100° C., from about 600° C. to about 900° C., 850° C.). Thepressure of the hydrogen (or hydrogen/inert gas mixture) can berelatively low (e.g., less than about one torr, less than about 1×10⁻³torr, less than about 1×10⁻⁶ torr) or relatively high (e.g., greaterthan about 1 torr, greater than about 100 torr, greater than about 760torr).

Without wishing to be bound by theory, it is believed that exposing thetextured substrate surface to a source of sulfur under these conditionscan result in the formation of a superstructure (e.g., a c(2×2)superstructure) of sulfur on the textured substrate surface. It isfurther believed that the superstructure can be effective in stabilizing(e.g., chemically and/or physically stabilizing) the surface of theintermediate layer.

While one approach to forming a sulfur superstructure has beendescribed, other methods of forming such superstructures can also beused. For example, a sulfur superstructure (e.g., c(2×2)) can be formedby applying an appropriate organic solution to the surface of theintermediate layer by heating to an appropriate temperature in anappropriate gas environment. It can also be obtained by allowing sulfur,which can be added to the substrate material, to diffuse to the surfaceof the substrate.

Moreover, while formation of a sulfur superstructure on the surface ofthe intermediate layer has been described, it is believed that othersuperstructures may also be effective in stabilizing (e.g., chemicallyand/or physically stabilizing) the surface. For example, it is believedthat an oxygen superstructure, a nitrogen superstructure, a carbonsuperstructure, a potassium superstructure, a cesium superstructure, alithium superstructure or a selenium superstructure disposed on thesurface may be effective in enhancing the stability of the surface.

The substrate may also be untextured, for example, using Hastelloy orother commercial metals.

Buffer Layer

In a second processing station 420, a buffer layer is formed on thetextured substrate.

Examples of buffer materials include metals and metal oxides, such assilver, nickel, TbO, CeO₂, yttria-stabilized zirconia (YSZ), Y₂O₃,Gd₂O₃, LaAlO₃, SrTiO₃, LaNiO₃, LaCuO.sub.3, SrRuO₃, NdGaO₃, NdAlO₃and/or nitrides as known to those skilled in the art.

In certain embodiments, an epitaxial buffer layer can be formed using alow vacuum vapor deposition process (e.g., a process performed at apressure of at least about 1×10³ torr). The process can include formingthe epitaxial layer using a relatively high velocity and/or focused gasbeam of buffer layer material.

The buffer layer material in the gas beam can have a velocity of greaterthan about one meter per second (e.g., greater than about 10 meters persecond or greater than about 100 meters per second). At least about 50%of the buffer layer material in the beam can be incident on the targetsurface (e.g., at least about 75% of the buffer layer material in thebeam can be incident on the target surface, or at least about 90% of thebuffer layer material in the beam can be incident on the targetsurface).

The method can include placing a target surface (e.g., a substratesurface or a buffer layer surface) in a low vacuum environment, andheating the target surface to a temperature which is greater than thethreshold temperature for forming an epitaxial layer of the desiredmaterial on the target surface in a high vacuum environment (e.g., lessthan about 1×10⁻³ torr, such as less than about 1×10⁻⁴ torr) underotherwise identical conditions. A gas beam containing the buffer layermaterial and optionally an inert carrier gas is directed at the targetsurface at a velocity of at least about one meter per second. Aconditioning gas is provided in the low vacuum environment. Theconditioning gas can be contained in the gas beam, or the conditioninggas can be introduced into the low vacuum environment in a differentmanner (e.g., leaked into the environment). The conditioning gas canreact with species (e.g., contaminants) present at the target surface toremove the species, which can promote the nucleation of the epitaxialbuffer layer.

The epitaxial buffer layer can be grown on a target surface using a lowvacuum (e.g., at least about 1×10⁻³ torr, at least about 0.1 torr, or atleast about 1 torr) at a surface temperature below the temperature usedto grow the epitaxial layer using physical vapor deposition at a highvacuum (e.g., at most about 1×10⁻⁴ torr). The temperature of the targetsurface can be, for example, from about 25° C. to about 800° C. (e.g.,from about 500° C. to about 800° C., or from about 500° C. to about 650°C.).

The epitaxial layer can be grown at a relatively fast rate, such as, forexample, at least about 50 Angstroms per second.

These methods are described in U.S. Pat. No. 6,027,564, issued Feb. 22,2000, and entitled “Low Vacuum Process for Producing Epitaxial Layers;”U.S. Pat. No. 6,022,832, issued Feb. 8, 2000, and entitled “Low VacuumProcess for Producing Superconductor Articles with Epitaxial Layers;”and/or commonly owned U.S. patent application Ser. No. 09/007,372 filedJan. 15, 1998, and entitled “Low Vacuum Process for Producing EpitaxialLayers of Semiconductor Material,” all of which are hereby incorporatedby reference.

In some embodiments, an epitaxial buffer layer can be deposited bysputtering from a metal or metal oxide target at a high throughput.Heating of the substrate can be accomplished by resistive heating orbias and electric potential to obtain an epitaxial morphology. Adeposition dwell may be used to form an oxide epitaxial film from ametal or metal oxide target.

The oxide layer typically present on substrates can be removed byexposure of the substrate surface to energetic ions within a reducingenvironment, also known as Ion Beam etching. Ion Beam etching can beused to clean the substrate prior to film deposition, by removingresidual oxide or impurities from the substrate, and producing anessentially oxide-free preferably biaxially textured substrate surface.This improves the contact between the substrate and subsequentlydeposited material. Energetic ions can be produced by various ion guns,for example, which accelerate ions such as Ar⁺ toward a substratesurface. Preferably, gridded ion sources with beam voltages greater than150 eV are utilized. Alternatively, a plasma can be established in aregion near the substrate surface. Within this region, ions chemicallyinteract with a substrate surface to remove material from that surface,including metal oxides, to produce substantially oxide-free metalsurface.

Another method to remove oxide layers from a substrate is toelectrically bias the substrate. If the substrate is made negative withrespect to the anode potential, it will be subjected to a steadybombardment by ions from the gas prior to the deposition (if the targetis shuttered) or during the entire film deposition. This ion bombardmentcan clean the substrate surface of absorbed gases that might otherwisebe incorporated in the film and also heat the substrate to elevateddeposition temperatures. Such ion bombardment can be furtheradvantageous by improving the density or smoothness of the epitaxialfilm.

Upon formation of an appropriately textured, substantially oxide-freesubstrate surface, deposition of a buffer layer can begin. One or morebuffer layers, each including a single metal or oxide layer, can beused. In some preferred embodiments, the substrate is allowed to passthrough an apparatus adapted to carry out steps of the deposition methodof these embodiments. For example, if the substrate is in the form of atape, the substrate can be passed linearly from a payout reel to atake-up reel, and steps can be performed on the substrate as it passesbetween the reels.

According to some embodiments, substrate materials are heated toelevated temperatures which are less than about 90% of the melting pointof the substrate material but greater than the threshold temperature forforming an epitaxial layer of the desired material on the substratematerial in a vacuum environment at the predetermined deposition rate.In order to form the appropriate buffer layer crystal structure andbuffer layer smoothness, high substrate temperatures are generallypreferred. Typical lower limit temperatures for the growth of oxidelayers on metal are approximately 200° C. to 800° C., preferably 500° C.to 800° C., and more preferably, 650° C. to 800° C. Various well-knownmethods such as radiative heating, convection heating, and conductionheating are suitable for short (2 cm to 10 cm) lengths of substrate, butfor longer (1 m to 100 m) lengths, these techniques may not be wellsuited. Also to obtain desired high throughput rates in a manufacturingprocess, the substrate must be moving or transferring between depositionstations during the process. According to particular embodiments, thesubstrates are heated by resistive heating, that is, by passing acurrent through the metal substrate, which is easily scaleable to longlength manufacturing processes. This approach works well whileinstantaneously allowing for rapid travel between these zones.Temperature control can be accomplished by using optical pyrometers andclosed loop feedback systems to control the power supplied to thesubstrate being heated. Current can be supplied to the substrate byelectrodes that contact the substrate in at least two different segmentsof the substrate. For example, if the substrate, in the form of a tape,is passed between reels, the reels themselves could act as electrodes.Alternatively, if guides are employed to transfer the substrate betweenreels, the guides could act as electrodes. The electrodes could also becompletely independent of any guides or reels as well. In some preferredembodiments, current is applied to the substrate tape between currentwheels.

In order that the deposition is carried out on a substrate that is atthe appropriate temperature, the metal or oxide material that isdeposited onto the substrate is desirably deposited in a region betweenthe current wheels. Because the current wheels can be efficient heatsinks and can thus cool the tape in regions proximate to the wheels,material is desirably not deposited in regions proximate to the wheels.In the case of sputtering, the charged material deposited onto thesubstrate is desirably not influenced by other charged surfaces ormaterials proximate to the sputter flux path. For this reason, thesputter chamber is preferably configured to place components andsurfaces which could influence or deflect the sputter flux, includingchamber walls, and other deposition elements, in locations distant fromthe deposition zone so that they do not alter the desired linear fluxpath and deposition of metal or metal oxide in regions of the tape atthe proper deposition temperature.

More details are provided in commonly owned U.S. patent application Ser.No. 09/500,701, filed on Feb. 9, 2000, and entitled “Oxide LayerMethod,” and commonly owned U.S. patent application Ser. No. 0/615,669,filed on Jul. 14, 2000, and entitled “Oxide Layer Method,” both of whichare hereby incorporated by reference in their entirety.

In preferred embodiments, three buffer layers are used. A layer of Y₂O₃or CeO₂ (e.g., from about 20 nanometers to about 75 nanometers thick) isdeposited (e.g., using electron beam evaporation) onto the substratesurface. A layer of YSZ (e.g., from about 0.20 nanometers about 700nanometers thick, such as about 75 nanometers thick) is deposited ontothe surface of the Y₂O₃ or CeO₂ layer using sputtering (e.g., usingmagnetron sputtering). A CeO₂ layer (e.g., about 20 nanometers thick) isdeposited (e.g., using magnetron sputtering) onto the YSZ surface. Thesurface of one or more of these layers can be chemically and/orthermally conditioned as described herein.

In certain embodiments, a buffer layer material can be prepared usingsolution phase techniques, including metalorganic deposition, which areknown to those skilled in the art. Such techniques are disclosed in, forexample, S. S. Shoup et al., J. Am. Cer. Soc., Vol. 81, 3019; D. Beachet al., Mat. Res. Soc. Symp. Proc., vol. 495, 263 (1988); M. Paranthamanet al., Superconductor Sci. Tech., vol. 12, 319 (1999); D. J. Lee etal., Japanese J. Appl. Phys., vol. 38, L178 (1999) and M. W. Rupich etal., I.E.E.E. Trans. on Appl. Supercon. vol. 9, 1527.

In certain embodiments, solution coating processes can be used fordeposition of one or a combination of any of the oxide layers ontextured substrates; however, they can be particularly applicable fordeposition of the initial (seed) layer on a textured metal substrate.The role of the seed layer is to provide 1) protection of the substratefrom oxidation during deposition of the next oxide layer when carriedout in an oxidizing atmosphere relative to the substrate (for example,magnetron sputter deposition of yttria-stabilized zirconia from an oxidetarget); and 2) an epitaxial template for growth of subsequent oxidelayers. In order to meet these requirements, the seed layer should growepitaxially over the entire surface of the metal substrate and be freeof any contaminants that may interfere with the deposition of subsequentepitaxial oxide layers.

In certain embodiments, the buffer layer can be formed using ion beamassisted deposition (IBAD). In this technique, a buffer layer materialis evaporated using, for example, electron beam evaporation, sputteringdeposition, or pulsed laser deposition while an ion beam (e.g., an argonion beam) is directed at a smooth amorphous surface of a substrate ontowhich the evaporated buffer layer material is deposited.

For example, the buffer layer can be formed by ion beam assisteddeposition by evaporating a buffer layer material having a rock-saltlike structure (e.g., a material having a rock salt structure, such asan oxide, including MgO, or a nitride) onto a smooth, amorphous surface(e.g., a surface having a root mean square roughness of less than about100 Angstroms) of a substrate so that the buffer layer material has asurface with substantial alignment (e.g., about 13° or less), bothin-plane and out-of-plane.

The conditions used during deposition of the buffer layer material caninclude, for example, a substrate temperature of from about 0° C. toabout 750° C. (e.g., from about 0° C. to about 400° C., from about roomtemperature to about 750° C., from about room temperature to about 400°C.), a deposition rate of from about 1.0 Angstrom per second to about4.4 Angstroms per second, an ion energy of from about 200 eV to about1200 eV, and/or an ion flux of from about 110 microamperes per squarecentimeter to about 120 microamperes per square centimeter.

In some embodiments, when using IBAD, the substrate is formed of amaterial having a polycrystalline, non-amorphous base structure (e.g., ametal alloy, such as a nickel alloy) with a smooth amorphous surfaceformed of a different material (e.g., Si₃N₄).

In certain embodiments, a plurality of buffer layers can be deposited byepitaxial growth on an original IBAD surface. Each buffer layer can havesubstantial alignment (e.g., about 13° or less), both in-plane andout-of-plane.

The formation of oxide buffer layers can be carried out so as to promotewetting of an underlying substrate layer. Additionally, in particularembodiments, the formation of metal oxide layers can be carried outusing metal alkoxide or carboxylate precursors (for example, “sol gel”precursors).

As described above, if desired, the buffer layer or layers can bepatterned either during or subsequent to their deposition.

Precursor Layer

Once the textured substrate including buffer layers is prepared, aprecursor solution is deposited at a station 430 as described above. Oneor more layers are deposited to form a precursor layer having thedesired thickness and overall composition.

Suitable precursor components include soluble compounds of one or morerare earth elements, one or more alkaline earth metals and one or moretransition metals. As used herein, “soluble compounds” of rare earthelements, alkaline earth metals and transition metals refers tocompounds of these metals that are capable of dissolving in the solventscontained in the precursor solution. Such compounds include, forexample, salts (e.g., nitrates, acetates, alkoxides, halides, sulfates,and trifluoroacetates), oxides and hydroxides of these metals. At leastone of the compounds is a fluorine-containing compound, such as thetrifluoroacetate.

Examples of metal salt solutions that can be used are as follows.

In some embodiments, the metal salt solution can have a relatively smallamount of free acid. In aqueous solutions, this can correspond to ametal salt solution with a relatively neutral pH (e.g., neither stronglyacidic nor strongly basic). The metal salt solution can be used toprepare multi-layer superconductors using a wide variety of materialsthat can be used as the underlying layer on which the superconductorlayer is formed.

The total free acid concentration of the metal salt solution can be lessthan about 1×10⁻³ molar (e.g., less than about 1×10⁻⁵ molar or about1×10⁻⁷ molar). Examples of free acids that can be contained in a metalsalt solution include trifluoroacetic acid, acetic acid, nitric acid,sulfuric acid, acids of iodides, acids of bromides and acids ofsulfates.

When the metal salt solution contains water, the precursor compositioncan have a pH of at least about 3 (e.g., at least about 5 or about 7).

In some embodiments, the metal salt solution can have a relatively lowwater content (e.g., less than about 50 volume percent water, less thanabout 35 volume percent water, less than about 25 volume percent water).

In general, the rare earth metal salt can be any rare earth metal saltthat is soluble in the solvent(s) contained in the precursor solutionand that, when being processed to form an intermediate (e.g., a metaloxyhalide intermediate), forms rare earth oxide(s) (e.g., Y₂O₃). Therare earth elements may be selected from the group of yttrium, cerium,neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium,erbium, thulium, ytterbium, and lutetium. Typically, the alkaline earthmetal is barium, strontium or calcium. Such salts can have, for example,the formulaM(O₂C—(CH₂)_(n)—CXX′X″)(O₂C—(CH₂)_(m)—CX′″X″″X′″″)(O₂C—(CH₂)_(p)—CX″″″X′″″″X″″″″)or M(OR)₃. M is the rare earth metal. n, m and p are each at least onebut less than a number that renders the salt insoluble in the solvent(s)(e.g., from one to ten). Each of X, X′, X″, X′″, X″″, X′″″, X″″″, X′″″″and X″″″″ is H, F, Cl, Br or I. R is a carbon containing group, whichcan be halogenated (e.g., CH₂CF₃) or nonhalogenated. Examples of suchsalts include nonhalogenated carboxylates, halogenated acetates (e.g.,trifluoroacetate, trichloroacetate, tribromoacetate, triiodoacetate),halogenated alkoxides, and nonhalogenated alkoxides. Examples of suchnonhalogenated carboxylates include nonhalogenated actetates (e.g.,M(O₂C—CH₃)₃). Generally, the alkaline earth metal salt can be anyalkaline earth metal salt that is soluble in the solvent(s) contained inthe precursor solution and that, when being processed to form anintermediate (e.g., a metal oxyhalide intermediate), forms an alkalineearth halide compound (e.g., BaF₂, BaCl₂, BaBr₂, BaI₂) prior to formingalkaline earth oxide(s) (e.g., BaO). Such salts can have, for example,the formula M′(O₂C—(CH₂)_(n)—CXX′X″)(O₂C—(CH₂)_(m)—CX′″X″″X′″″) orM′(OR)₂. M′ is the alkaline earth metal. n and m are each at least onebut less than a number that renders the salt insoluble in the solvent(s)(e.g., from one to ten). Each of X, X′, X″, X′″, X″″ and X′″″ is H, F,Cl, B or, I. R can be a halogenated or nonhalogenated carbon containinggroup. Examples of such salts include halogenated acetates (e.g.,trifluoroacetate, trichloroacetate, tribromoacetate, triiodoacetate).Generally, the transition metal is copper. The transition metal saltshould be soluble in the solvent(s) contained in the precursor solution.In one or more embodiments of the present invention, the rare earth andthe alkaline earth elements can form a metal or mixed metal oxyfluoridein place of or in addition to a rare earth oxide and an alkaline earthfluoride.

Suitable copper precursor solutions contain a copper salt that issoluble at the appropriate concentration in the solvent(s). Suchcompounds include copper nitrates, carboxylates, alkoxides, halides,sulfates or trifluoroacetates. Preferably, during conversion of theprecursor to the intermediate (e.g., metal oxyhalide), minimalcross-linking occurs between discrete transition metal molecules (e.g.,copper molecules). Such transition metals salts can have, for example,the formulaM″(CXX′X″—CO(CH)_(a)CO—CX′″X″″X′″″)(CX″″″X′″″″X″″″″—CO(CH)_(b)COCX′″″″″X″″″″″X′″″″″″),M″(O₂C—(CH₂)_(n)—CXX′X″)(O₂C—(CH₂)_(m)—CX′″X″″X′″″) or M″(OR)₂. M″ isthe transition metal. a and b are each at least one but less than anumber that renders the salt insoluble in the solvent(s) (e.g., from oneto five). Generally, n and m are each at least one but less than anumber that renders the salt insoluble in the solvent(s) (e.g., from oneto ten). Each of X, X′, X″, X′″, X″″, X′″″, X″″″, X′″″″, X″″″″, X′″″″″,X″″″″″, X′″″″″″ is H, F, Cl, Br or I. R is a carbon containing group,which can be halogenated (e.g., CH₂CF₃) or nonhalogenated. These saltsinclude, for example, nonhalogenated actetates (e.g., M″(O₂C—CH₃)₂),halogenated acetates, halogenated alkoxides, and nonhalogenatedalkoxides. Examples of such salts include copper trichloroacetate,copper tribromoacetate, copper triiodoacetate, Cu(CH₃COCHCOCF₃)₂,Cu(OOCC₇H₁₅)₂, Cu(CF₃COCHCOF₃)₂, Cu(CH₃COCHCOCH₃)₂,Cu(CH₃CH₂CO₂CHCOCH₃)₂, CuO(C₅H₆N)₂ and Cu₃O₃Ba₂(O—CH₂CF₃)₄. A suitablecompound is copper proprionate. An example of a nonhalogenatedpropionate salt of a transition metal is Cu(O₂CC₂H₅)₂. In someembodiments, the transition metal salt is a simple salt, such as coppersulfate, copper nitrate, copper iodide and/or copper oxylate. In someembodiments, n and/or m can have the value zero. In certain embodiments,a and/or b can have the value zero. An illustrative and nonlimiting listof Lewis bases includes nitrogen-containing compounds, such as ammoniaand amines. Examples of amines include CH₃CN, C₅H₅N and R₁R₂R₃N. Each ofR₁R₂R₃ is independently H, an alkyl group (e.g., a straight chainedalkyl group, a branched alkyl group, an aliphatic alkyl group, anon-aliphatic alkyl group and/or a substituted alkyl group) or the like.Without wishing to be bound by theory, it is believed that the presenceof a Lewis base in the metal salt solution can reduce cross-linking ofcopper during intermediate formation. It is believed that this isachieved because a Lewis base can coordinate (e.g., selectivecoordinate) with copper ions, thereby reducing the ability of copper tocross-link.

While the precursor solution typically contains stoichiometric amountsof the component metal compounds, i.e., 3:2:1 Cu:Ba:RE, in someembodiments an excess of copper or a deficiency of barium is used. Theratio of the transition metal to the alkaline earth metal can be greaterthan 1.5, and the precursor solution can include at least about 5 mol %excess copper, or at least about 20 mol % excess copper.

In addition to precursor components for the formation of arare-earth/alkaline-earth-metal/transition-metal oxide, the precursorsolution may include additive components and/or dopant components forthe formation of flux pinning sites is used in a solution-based methodto obtain a superconducting film having pinning centers. The additivecompound can be metal compounds, such as soluble compounds of rareearths, alkaline earths or transition metals, cerium, zirconium, silver,aluminum, or magnesium, that form metal oxide or metal in the oxidesuperconductor film. The precursor solution can provide a dopant metalthat partially substitutes for a metal of the precursor component of theprecursor solution. Generally, a dopant component can be any metalcompound that is soluble in the solvent(s) contained in the precursorsolution and that, when processed to form an oxide superconductor,provided a dopant metal that substitutes for an element of the oxidesuperconductor.

The solvent or combination of solvents used in the precursor solutioncan include any solvent or combination of solvents capable of dissolvingthe metal salts (e.g., metal carboxylate(s)). Such solvents include, forexample, alcohols or acids, including methanol, ethanol, isopropanol andbutanol, propionic acid or water.

In embodiments in which the metal salt solution containstrifluoroacetate ion and an alkaline earth metal cation (e.g., barium),the total amount of trifluoroacetate ion can be selected so that themole ratio of fluorine contained in the metal salt solution (e.g., inthe form of trifluoroacetate) to the alkaline earth metal (e.g., bariumions) contained in the metal salt solution is at least about 2:1 (e.g.,from about 2:1 to about 18.5:1, or from about 2:1 to about 10:1).

The methods of disposing the superconducting composition on theunderlying layer (e.g., on a surface of a substrate, such as a substratehaving an alloy layer with one or more buffer layers disposed thereon)include spin coating, dip coating, slot coating, web coating and othertechniques known in the art.

Decomposition of the Precursor Layer

At a subsequent station 440, the precursor components are decomposed.The conversion of the precursor components into an oxide superconductoris carried out as has been previously reported for continuous thickprecursor films. In the case of precursor components including at leastone fluoride-containing salt, the first step of the heating step isperformed to decompose the metalorganic molecules to one or moreoxyfluoride intermediates of the desired superconductor material.

An intermediate oxyfluoride film is considered to be any film that is aprecursor to a rare earth metal-alkaline earth metal-transition metaloxide superconductor (hereinafter “RE-123”) film that is comprised of(1) a mixture of BaF₂, a rare earth oxide or fluoride and/or transitionmetal, transition metal oxide or transition metal fluoride, (2) amixture of a compound comprised of a RE-Ba—O—F phase, a rare earth oxideor fluoride and/or transition metal oxide or fluoride, or (3) as amixture of a compound comprised of a Ba—O—F phase, rare earth oxides orfluorides and/or transition metal oxide or fluoride. The intermediatefilm can then be further processed to form a RE-123 oxide superconductorfilm. The oxide superconductor film also indicates a small, butdetectable, fluoride residue.

Typically, the initial temperature in this step is about roomtemperature, and the final temperature is from about 190° C. to about210° C., preferably to a temperature to about 200° C. Preferably, thisstep is performed using a temperature ramp of at least about 5° C. perminute, more preferably a temperature ramp of at least about 10° C. perminute, and most preferably a temperature ramp of at least about 15° C.per minute. During this step, the partial pressure of water vapor in thenominal gas environment is preferably maintained at from about 5 torr toabout 50 torr, more preferably at from about 5 torr to about 30 torr,and most preferably at from about 20 torr to about 30 torr. The partialpressure of oxygen in the nominal gas environment is maintained at fromabout 0.1 torr to about 760 torr and preferably at about 730-740 torr.

Heating is then continued to a temperature of from about 200° C. toabout 290° C. using a temperature ramp of from about 0.05° C. per minuteto about 5° C. per minute (e.g., from about 0.5° C. per minute to about1° C. per minute). Preferably, the gas environment during this heatingstep is substantially the same as the nominal gas environment used whenthe sample is heated to from the initial temperature to from about 190°C. to about 215° C.

Heating is further continued to a temperature of about 650° C., or morepreferably to a temperature of about 400° C., to form the oxyfluorideintermediate. This step is preferably performed using a temperature rampof at least about 2° C. per minute, more preferably at least about 3° C.per minute, and most preferably at least about 5° C. per minute.Preferably, the gas environment during this heating step issubstantially the same as the nominal gas environment used when thesample is heated to from the initial temperature to from about 190° C.to about 215° C.

In alternate embodiments, barium fluoride is formed by heating the driedsolution from an initial temperature (e.g., room temperature) to atemperature of from about 190° C. to about 215° C. (e.g., about 210° C.)in a water vapor pressure of from about 5 torr to about 50 torr watervapor (e.g., from about 5 torr to about 30 torr water vapor, or fromabout 10 torr to about 25 torr water vapor). The nominal partialpressure of oxygen can be, for example, from about 0.1 torr to about 760torr. In these embodiments, heating is then continued to a temperatureof from about 220° C. to about 290° C. (e.g., about 220° C.) in a watervapor pressure of from about 5 torr to about 50 torr water vapor (e.g.,from about 5 torr to about 30 torr water vapor, or from about 10 torr toabout 25 torr water vapor). The nominal partial pressure of oxygen canbe, for example, from about 0.1 torr to about 760 torr. This is followedby heating to about 400° C. at a rate of at least about 2° C. per minute(e.g., at least about 3° C. per minute, or at least about 5° C. perminute) in a water vapor pressure of from about 5 torr to about 50 torrwater vapor (e.g., from about 5 torr to about 30 torr water vapor, orfrom about 10 torr to about 25 torr water vapor) to form bariumfluoride. The nominal partial pressure of oxygen can be, for example,from about 0.1 torr to about 760 torr.

In certain embodiments, heating the dried solution to form bariumfluoride can include putting the coated sample in a pre-heated furnace(e.g., at a temperature of at least about 100° C., at least about 150°C., at least about 200° C., at most about 300° C., at most about 250°C., about 200° C.). The gas environment in the furnace can have, forexample, a total gas pressure of about 760 torr, a predetermined partialpressure of water vapor (e.g. at least about 10 torr, at least about 15torr, at most about 25 torr, at most about 20 torr, about 17 torr) withthe balance being molecular oxygen. After the coated sample reaches thefurnace temperature, the furnace temperature can be increased (e.g., toat least about 225° C., to at least about 240° C., to at most about 275°C., to at most about 260° C., about 250° C.) at a predeterminedtemperature ramp rate (e.g., at least about 0.5° C. per minute, at leastabout 0.75° C. per minute, at most about 2° C. per minute, at most about1.5° C. per minute, about 1° C. per minute). This step can be performedwith the same nominal gas environment used in the first heating step.The temperature of the furnace can then be further increased (e.g., toat least about 350° C., to at least about 375° C., to at most about 450°C., to at most about 425° C., about 450° C.) at a predeterminedtemperature ramp rate (e.g., at least about 5° C. per minute, at leastabout 8° C. per minute, at most about 20° C. per minute, at most about12° C. per minute, about 10° C. per minute). This step can be performedwith the same nominal gas environment used in the first heating step.

The foregoing treatments of a metal salt solution can result in anoxyfluoride intermediate film in which the constituent metal oxides andmetal fluorides are homogeneously distributed throughout the film.Preferably, the precursor has a relatively low defect density and isessentially free of cracks through the intermediate thickness. Whilesolution chemistry for barium fluoride formation has been disclosed,other methods can also be used for other precursor solutions.

Forming the Oxide Superconductor

The superconductor intermediate film can then be heated to form thedesired superconductor layer at a further processing station 450.Typically, this step is performed by heating from about room temperatureto a temperature of from about 700° C. to about 825° C., preferably to atemperature of about 740° C. to 800° C. and more preferably to atemperature of about 750° C. to about 790° C., at a temperature ramp ofabout greater than 25° C. per minute, preferably at a temperature rateof about greater than 100° C. per minute and more preferably at atemperature rate about greater than 200° C. per minute. This step canalso start from the final temperature of about 400-650° C. used to formthe intermediate oxyfluoride film. During this step, a process gas isflowed over the film surface to supply the gaseous reactants to the filmand to remove the gaseous reaction products from the film. The nominalgas environment during this step has a total pressure of about 0.1 torrto about 760 torr and is comprised of about 0.09 torr to about 50 torroxygen and about 0.01 torr to about 150 torr water vapor and about 0torr to about 750 torr of an inert gas (nitrogen or argon). Morepreferably, the nominal gas environment has a total pressure of about0.15 torr to about 5 torr and includes about 0.1 torr to about 1 torroxygen and about 0.05 torr to about 4 torr water vapor.

The film is then held at a temperature of about 700° C.-825° C.,preferably at a temperature of about 740° C. to 800° C. and morepreferably at a temperature of about 750° C. to about 790° C., for atime of about at least 5 minutes to about 120 minutes, preferably for atime of at least about 15 minutes to about 60 minutes, and morepreferably for a time of at least about 15 minutes to about 30 minutes.During this step, a process gas is flowed over the film surface tosupply the gaseous reactants to the film and to remove the gaseousreaction products from the film. The nominal gas environment during thisstep has a total pressure of about 0.1 torr to about 760 torr and iscomprised of about 0.09 torr to about 50 torr oxygen and about 0.01 torrto about 150 torr water vapor and about 0 torr to about 750 torr of aninert gas (nitrogen or argon). More preferably, the nominal gasenvironment has a total pressure of about 0.15 torr to about 5 torr andis comprised of about 0.1 torr to about 1 torr oxygen and about 0.05torr to about 4 torr water vapor.

The film is then cooled to room temperature in a nominal gas environmentwith an oxygen pressure of about 0.05 torr to about 150 torr, preferablyabout 0.1 torr to about 0.5 torr and more preferably from about 0.1 torrto about 0.2 torr.

The resultant superconductor layer is well ordered (e.g., biaxiallytextured in plane, or c-axis out of plane and biaxially textured inplane). In embodiments, the bulk of the superconductor material isbiaxially textured. A superconductor layer can be at least about onemicrometer thick (e.g., at least about two micrometers thick, at leastabout three micrometers thick, at least about four micrometers thick, atleast about five micrometers thick). The oxide superconductor has ac-axis orientation that is substantially constant across its width, thec-axis orientation of the superconductor being substantiallyperpendicular to the surface of the wire or tape.

The superconductor layer can also be deposited in-situ (no precursordeposition and separate reaction steps) by laser ablation, MOCVD, orother techniques known in the art.

Further Processing

Further processing by cap layer deposition at station 460, oxygen annealat station 470, and splicing to a second wire at station 490 are carriedout. By splicing wires together using low resistance, mechanicallyrobust joints, wires of length that is useable in a current carryingapplication without damage to the brittle oxide superconductor film areproduced.

Assuming that the wires being joined were not previously laminated tostabilizer strips, the spliced wires can then optionally be laminatedbetween stabilizer strips which can provide additional thermal andmechanical stability, as well as seal the wire to the environment. FIG.3C illustrates an exemplary system and method that can be used tolaminate stabilizer strips to a joined wire assembly such as thatillustrated in FIGS. 2A and 2B, to result in a laminated joined wireassembly such as that illustrated in FIGS. 2C and 2D. The finishedjoined, laminated article is formed by feeding a joined wire assemblysuch as that illustrated in FIGS. 2A and 2B off of reel 810 into a bathof filler 890. A first stabilizer strip is fed off of reel 850, and asecond stabilizer strip is fed off of reel 851, also into filler bath890. The filler simultaneously surrounds the joined HTS wire being fedfrom reel 810, and also laminates it to the stabilizer strips being fedfrom reels 850 and 851. Die 830 merges and consolidates the wire andstabilizers into a finished superconducting wire such as thatillustrated in FIGS. 2C and 2D.

Alternately, the system and method illustrated in FIG. 3C can be used tolaminate stabilizer strips to individual HTS wires before they arespliced, resulting in an assembly such as that illustrated in FIGS. 2Eand 2F. The system and method of FIG. 3C could be readily adapted foreither purpose by one skilled in the art.

EXAMPLES

Low resistance conductive bridge splices were made with overlap lengthsin the 10 to 20 cm range to connect reinforced YBCO coated conductortapes (i.e., wires including stabilizer strips on either side of eachsegment of spliced wire, such as that illustrated in FIGS. 2E-2F). Theexemplary spliced wires had either copper or stainless steel stabilizerstrips, and were formed with a variety of solders, as described ingreater detail below.

In general, the example conductive bridge splices exhibited totalresistances well below the 200 nano-ohm target level at 7K (<100 nanoohm per lap joint). They were also found to be well aligned, robust andtolerate double bending below 100 cm diameter without exhibitingsignificant Ic degradation.

The following example outlines a process for making a 100 mm overlapstrap splice. To make overlaps of various lengths replace 100 mm withthe target length and change the solder amount proportionally. Thepretin length will be 10 mm longer than the overlap length. Pretinningsolder can be useful for making splices; pretinning can prepare thesurfaces of the wires, thus improving the resulting mechanical andelectrical bond.

Example Process Parameters for Making Strap Splice, Using Indium orIn—Sn Solder

Solder: Indium or In—Sn.

Soldering Iron temperature: 341° F. to 381° F.

Soldering Sled temperature: 164° C. to 179° C.

Solder Sled pressure: 5-25 pounds.

Strap Length: Greater than or equal to 0.1 m plus overlap length times2. Typically a 0.7 meter strap length yields a strap splice overlap of100 mm.

Example Procedure for Making a Strap Splice with a 100 mm OverlapLength, Using Indium or In—Sn Solder

(1) Identify the HTS side of the two wires to be joined.

(2) Cut 0.7 meter section off one or the wires to make the strap.

(3) Write the wire number on the HTS side of both the wire and thestrap.

(4) Apply flux to the HTS side of the wire.

(5) Using ˜ 3/32″ of 0.040″ diameter Indium solder pretin the HTS sideof the payoff wire for a length of 110 mm.

(6) Excess Indium should be left on the tip of the wire.

(7) Cut off the excess Indium. This will be a blob on the end of thewire.

(8) Place a 45° Chamfer on the end of the wire on both edges.

(9) Measure 100 mm from the tip of the wire and mark the wire on theuntinned side.

(10) Repeat this process for both ends of the strap and the take-upwire.

(11) Place take up wire into the solder sled fixture with the HTS sideup.

(12) Apply flux to the surface of the Take-up wire.

(13) Apply flux to the HTS side of the strap.

(14) Place the HTS side of the strap unto the HTS side of the take-upwire aligning the 100 mm mark with the tip of the take-up wire.

(15) Using the solder sled, solder the two pieces together according towork instructions.

(16) After the two sections are soldered together remove wire fromsolder sled fixture. One overlap is complete.

(17) Repeat steps 9 to 11 to solder the strap to the other wire. In thiscase the strap will be on the take-up side.

Example Process Parameters for Making Strap Splice Ramp, Using IndiumSolder

Solder: Indium.

Soldering Iron temperature: 341° F. to 381° F.

Example Procedure for Making Ramps at Both Ends of the Overlap Joint,Using Indium Solder

(1) Apply ˜ 3/32″ of 0.040″ diameter Indium solder to the solderingiron.

(2) Then apply the soldering iron to the tip of the strap to form a ballof solder that spans the tip of the strap to the wire.

(3) The tip is held in place using an orange stick to make sure thestrap tip does not rise off the wire.

(4) Soldering iron is held in place until the indium wets both the strapand the wire which takes ˜30 seconds.

(5) Quickly remove soldering iron. At this point a ball of solder shouldspan the step formed by the tip of the strap and the wire.

(6) At this point the excess solder is removed from the joint region.This is done using a knife held in such a way that the approach angle is20° or less.

(7) The knife is then moved through the solder to create the ramp.

(8) Steps 1 to 7 are repeated 3 more times so that all wire ends arefirmly attached to the base wire. This prevents the separation along theHTS layer under bend conditions. This also seals the end of the wirepreventing the YBCO layer from reacting with water in the atmosphere anddegrading.

The results presented below are for example splices made with tapes thatwere laminated with either copper or stainless steel stabilizer strips,with splice lengths from 25 mm to 200 mm long. The phrase “HTS to HTSoverlap” is intended to mean that the HTS “sides” of two stabilized HTSwires are overlapped and spliced together as illustrated in FIGS. 2E and2F, e.g., without a substrate interposed between the HTS layers of twojoined stabilized wires. The phrase “HTS to substrate overlap” isintended to mean that the HTS “side” of one HTS wire is overlapped andspliced to the substrate “side” of another HTS wire, e.g., with a singlesubstrate interposed between the HTS layers of two joined stabilizedwires.

Electrical Results

HTS to HTS overlap resistance versus HTS to substrate overlap resistanceis reported in Table 1 and in Table 2. These overlaps were made usingYBCO-based HTS wires that were each stabilized with two copperstabilizer strips, and then spliced together. Individual measurements aswell as statistics are given for each case. The HTS to HTS overlap has aresistance that is 80 times lower than the HTS to substrate overlap.

HTS to HTS overlaps were made with overlap lengths of 50, 100, 125, and150 mm in length. These conditions are reported in Table 3. Theseoverlaps were made using 4.4 mm wide YBCO-based HTS wires that were eachstabilized with two stainless steel stabilizer strips, and then splicedtogether. Only HTS to HTS overlaps were made (no comparison of HTS tosubstrate overlap is provided).

FIG. 5 shows the measured relationship of overlap length to resistancefor joined HTS wires according to the embodiment of FIGS. 2E-2F, formedas described using the above example, using Indium solder to splice thewires together and with Pb—Sn solder bonding stainless steel stabilizerstrips to each individual HTS wire. Results are plotted as 1/L, where Lis the approximate overlap length. In general, the longer the splice(i.e., the smaller 1/L) the lower the measured resistance through thejoint; and the shorter the splice (i.e., the larger 1/L) the higher themeasured resistance through the joint. However, as can be seen in FIG.5, the measured resistances are slightly higher than calculated values.This deviation may be caused by the alloying of the PB—Sn laminationsolder with the Indium solder used to join the two elements togetherand/or deviations in lamination solder layer thickness and/or laminathickness and/or wire width and/or overlap tolerances.

Table 4 shows the resistance of 125 mm overlaps made using variousprocessing conditions. In—Sn solder results are also shown. As the dataillustrate, the resistance levels are fairly robust to processingconditions.

TABLE 1 Processing conditions and resistance results for HTS to HTSoverlaps made with copper laminated 4.4 mm wide tapes. Splice overlaplength is 25 mm long. Strap length is 25 mm. Resistance is given interms of nano-ohms pre overlap. A strap splice resistance is the sum ofthe two overlap resistances. Set points Resist- Solder Solder anceSplice iron sled Splice nano Wire number Number ° F. ° C. Ramps typeohms CC218-SL5-1 1 371 184 Yes F-F 27 2 371 184 Yes F-F 23 3 371 184 YesF-F 25 4 371 184 Yes F-F 33 CC218-SL5-25 1 351 179 Yes F-F 15 2 351 179Yes F-F 20 3 351 179 Yes F-F 10 4 351 179 Yes F-F 17 CC218-SL5-21 1 341169 No F-F 23 2 341 169 No F-F 13 3 331 164 No F-F 15 4 331 164 No F-F20 CC218-SL5-30 1 341 169 Yes F-F 17 2 341 169 Yes F-F 22 3 331 164 YesF-F 25 4 331 164 Yes F-F 26 CC218-SL4-2 1 341 169 Yes F-F 20 2 341 169Yes F-F 25 3 341 169 Yes F-F 21 4 341 169 Yes F-F 21 CC218-SL4-12 1 341169 No F-F 24 2 341 169 No F-F 23 3 341 169 No F-F 20 4 341 169 No F-F16 CC218-SL4-9 1 341 169 Yes F-F 26 2 341 169 Yes F-F 43 3 341 169 YesF-F 29 4 341 169 Yes F-F 32 CC218-SL5-32 1 341 169 Yes F-F 15 2 341 169Yes F-F 30 3 341 169 Yes F-F 8 4 341 169 Yes F-F 22 CC218-SL5-17 1 341169 Yes F-F 16 2 341 169 Yes F-F 41 3 341 169 Yes F-F 29 4 341 169 YesF-F N/A Average 22.6 8.0 43.0 Stdev 7.6

TABLE 2 Processing conditions and resistance results for HTS toSubstrate overlaps made with copper laminated 4.4 mm wide tapes. Spliceoverlap length is 25 mm long. Strap length is 75 mm. Resistance is givenin terms of nano-ohms pre overlap. A strap splice resistance is the sumof the two overlap resistances. Set points Resist- Solder Solder anceSplice iron sled Splice nano Wire number Number ° F. ° C. Ramps typeohms CC218-SL5-8 1 371 184 Yes F-B 1498 2 371 184 Yes F-B 1478 3 371 184Yes F-B 1430 4 371 184 Yes F-B 1409 CC218-SL5-2 1 361 184 No F-B 2416 2361 184 No F-B 2077 3 361 184 No F-B 1422 4 361 184 No F-B 1605CC218-SL5- 1 351 179 No F-B 1781 22 2 351 179 No F-B 1405 3 351 174 NoF-B 1481 4 351 174 No F-B 1624 CC218-SL4-4 1 351 179 No F-B 1934 2 351179 No F-B 1427 3 351 174 No F-B 4 351 174 No F-B 2089 Average 1672 Min1405 Max 2416 Stdev 316.8

TABLE 3 Processing conditions and resistance results for HTS to HTSoverlaps made with stainless steel laminated 4.4 mm wide tapes. Spliceoverlap length is varied. Only individual overlaps were made for thesetests. Resistance is given in terms of nano-ohms pre overlap. Strapsplice resistance is the sum of the two overlap resistances. Set pointsSolder Solder Splice Wire iron sled Solder Splice length number ° F. °C. amount type mm Comments CC249SL6 361 169 ¼ tip FF 50 Herm 1 50 mm361° F. CC249SL6 361 169 ½ tip FF 100 Herm 2 100 mm 361° F. CC249SL6 361169 ¾ tip FF 150 Herm 2 150 mm 361° F. CC249SL1 361 169 ¾ tip FF 125Herm 2 125 mm 361° F. CC249SL4 371 179 ¾ tip FF 125 Herm 2 125 mm 371°F. CC249SL1 361 169 ¾ tip FF 125 Herm 2 125 mm 361° In—Sn CC249SL6 361169 ¾ tip FF 125 Herm 2 361° F. Ramps

TABLE 4 Statistics for Example 125 mm splices. Resistance Average MaxMin STDEV Nano- Nano- Nano- Nano- Splice type Ohms Ohms Ohms Ohms Herm 2361° F. 64.8 71 59 3.74 Herm 2 361° F. In—Sn 58.9 66 51 3.65 Herm 2 361°F. Ramps 62.6 77 57 7.00 Herm 2 371° F. 63.8 68 59 3.41 All 125 mmsplices 62.4 77 51 4.97

Mechanical Results

The example strap splices were tested for double bend properties(forward and reverse bend and then measure) and twist testing. FIG. 6shows the double bend test results for selected HTS to HTS splices madefrom the copper laminated 4.4 mm wide YBCO wire with an overlap of 25mm, which are listed in Table 1 (wires denoted CC218-SL5-21 andCC218-SL4-2), as a function of bend diameter. Also plotted is thespecification for brass hermetic wire of greater than 95% Ic retentionafter a 200 mm double bend diameter. Note that all eight splices hadseen four double bends after receiving the 2″ diameter bend. This testshows that the strap splice can retain 95% of its Ic with a double bendof 75 mm.

The mechanical results shown in FIGS. 7, 8, and 9 are for selected HTSto HTS splices made from the copper laminated 4.4 mm wide YBCO wire withan overlap of 25 mm, which are listed in Table 1 (wires denotedCC218-SL4-9 and CC218-SL4-12). In FIGS. 7, 8, and 9, respectively, thespliced wires were wrapped around a former (a cylinder of knowndiameter, as known to those of skill in the art) with 25 mm 20 mm or 16mm diameter. The Ic retention for the spliced wire was measured as afunction of pitch length (length over which the wire is wrapped aroundthe former diameter) with 10 pounds of tension. The retained Ic wasmeasured over a 10 cm tap length at 77 K using a one microvolt/cmcriteria. In all cases the strap splice made with YBCO wire met orexceeded the mechanical properties of BSCCO wire. In each plot, averageminus-standard deviations is an indicator of minimum Ic retention overtime.

The wind tolerance of a wire can be measured using the following steps:

(1) Test Ic of the spliced wire using a 30 cm (single overlap) and 1meter tap length for the voltage taps.

(2) Attach the spliced wire (having a total length of about 1.35 meters)to a mandrel of desired diameter (e.g., 42 mm).

(3) Attach a desired weight to the free end of the spliced wire (e.g.,10 pounds).

(4) Allow the weight and spliced wire to hang freely from the mandrel.

(5) Adjust the pitch of the mandrel (with respect to gravity) to allowthe wire to wind onto the mandrel at the desired pitch.

(6) Wind the spliced wire onto the mandrel.

(7) Unwind the spliced wire.

(8) Test the Ic of the spliced wire using a 30 cm (single overlap) and 1meter tap length for the voltage taps.

(9) Calculate the retained Ic by dividing the second Ic measurement (Icfinal) by the first Ic (Ic initial). If the resulting value is greaterthan about 0.95, the spliced wire is judged to have retained asufficient Ic for normal use.

Other exemplary strap splices made using 4.4 mm wide YBCO-based HTS wirethat were laminated with stainless steel stabilizer strips using indiumsolder, according to the embodiment of FIGS. 2E-2F and using theexemplary method described above, and tested for double bend tolerance.FIGS. 10-12 show the mechanical performance of selected splices withoverlap lengths of 50, 100 and 150 mm (spliced wire CC249-SL6, listed inTable 3). In all cases the exemplary splices retained greater than 95%of their Ic after receiving a double bend down to 42 mm diameter.

The bend tolerance of a wire can be measured using the following steps:

(1) Test Ic of the spliced wire using a 30 cm (single overlap) and 1meter tap length for the voltage taps.

(2) Attach the spliced wire (having a total length of about 1.35 meters)to a mandrel of desired diameter (e.g., 42 mm).

(3) Attach a desired weight to the free end of the spliced wire (e.g.,10 pounds).

(4) Allow the weight and spliced wire to hang freely from the mandrel.

(5) Wind the spliced wire onto the mandrel, laying the turns within 1 cmof each other.

(6) Unwind the spliced wire.

(7) Turn the spliced wire over, such that the opposite face of the wire(the one that had not been in contact with the mandrel) will now be incontact with the mandrel.

(8) Wind the spliced wire onto the mandrel, laying the turns within 1 cmof each other.

(9) Unwind the spliced wire.

(10) Test the Ic of the spliced wire using a 30 cm (single overlap) and1 meter tap length for the voltage taps.

(11) Calculate the retained Ic by dividing the second Ic measurement (Icfinal) by the first Ic (Ic initial). If the resulting value is greaterthan about 0.95, the spliced wire is judged to have retained asufficient Ic for normal use.

FIG. 10 shows double bend mechanical results for stainless steellaminated YBCO wire strap splices (wire CC249-SL6) with an overlaplength of 150 mm.

FIG. 11 shows double bend mechanical results for stainless steellaminated YBCO HTS wire strap splices (wire CC249-SL6) with an overlaplength of 100 mm.

FIG. 12 shows double bend mechanical results for stainless steellaminated YBCO wire strap splices (wire CC249-SL6) with an overlaplength of 50 mm.

Another mechanical result is the performance of the ramp. FIG. 13 is amicrograph of an exemplary spliced wire similar to that shown in FIGS.2E-2F, using pure indium solder 1340 to join conductive bridge 1330 towire 1320, but with no solder “ramps” (e.g., edge seal 250″ similar tothat shown in FIG. 2E). FIG. 13 shows the tip of an overlap that wasdouble bent over a 100 mm mandrel, in which the lift off in the HTSlayer can clearly be seen. Specifically, the conductive bridge 1330includes an upper stabilizer layer 1370, a layer of filler 1380 bondingthe stabilizer to substrate 1310, a buffer/HTS/cap layer assembly 1331,and lower stabilizer 1371. The wire 1320 is similarly constructed, andhas upper stabilizer layer 1373 which is bonded to the lower stabilizer1371 of conductive bridge 1330 with solder 1340. As FIG. 13 clearlyshows, after double blending over a 100 mm mandrel, the buffer/HTS/caplayer assembly 1331 separates from substrate 1310, leaving a large gap1300 between the two. This can results in a significant degradation inperformance. The mechanical degradation can be avoided by appropriatelyselecting materials and/or architecture of the wire.

FIG. 14 is a micrograph of a similar structure to that shown in FIG. 13,but which includes a solder “ramp” (e.g., edge seal 250″ similar to thatshown in FIG. 2E). FIG. 14 shows two separate spliced wire assemblies,each of which was constructed separately from each other, which arearranged next to each other in the micrograph. The following discussionfocuses on “Spliced wire 2”, which appears in the bottom of themicrograph, but applies equally to “Spliced wire 1,” in the top of themicrograph. Like the spliced wire shown in FIG. 13, Spliced wire 2includes a conductive bridge 1430 that is spliced to a wire 1420 withsolder 1440. The conductive bridge 1430 includes an upper stabilizerlayer 1470, a layer of filler 1480 bonding the stabilizer to substrate1410, a buffer/HTS/cap layer assembly 1431, and lower stabilizer 1471.The wire 1420 is similarly constructed, and has upper stabilizer layer1473 which is bonded to the lower stabilizer 1471 of conductive bridge1430 with solder 1440. Unlike the example shown in FIG. 13, the examplein FIG. 14 includes a solder “ramp” 1450 that both seals the end ofconductive bridge 1430 and improves the mechanical performance of thejoint.

FIG. 14 is a micrograph of a pure Indium splice with solder ramps. FIG.14 shows the tip of an overlap receiving a double bend over a 50 mmmandrel, in which the lack of separation of the HTS layer can clearly beseen. This demonstrates that the ramp helps to provide a strap splicethat is mechanically and environmentally robust.

Example Process Parameters for Making Strap Splice, Using Sn—Pb orSn—Pb—Ag Solder

Solder: Sn—Pb or Sn—Pb—Ag.

Soldering Iron temperature: 400° F. to 450° F.

Soldering Sled temperature: 205° C. to 220° C.

Solder Sled pressure: 5-25 pounds.

Strap Length: Greater than or equal to 0.1 m plus overlap length times2. Typically a 0.7 meter strap length yields a strap splice overlap of100 mm.

Example Procedure for Making a Strap Splice with a 100 mm OverlapLength, Using Sn—Pb or Sn—Pb—Ag Solder

1) Identify the HTS side of the two wires to be joined.

2) Cut 0.7 meter section off one or the wires to make the strap.

3) Write the wire number on the HTS side of both the wire and the strap.

4) Apply flux to the HTS side of the wire.

5) Using ˜ 6/32″ of 0.032″ diameter 60 Sn-40 Pb solder pretin the HTSside of the payoff wire for a length of 110 mm.

6) Excess 60 Sn-40 Pb should be left on the tip of the wire.

7) Cut off the excess 60 Sn-40 Pb. This will be a blob on the end of thewire.

8) Place a 45° Chamfer on the end of the wire on both edges.

9) Measure 100 mm from the tip of the wire and mark the wire on theuntinned side.

10) Repeat this process for both ends of the strap and the take-up wire.

11) Place take up wire into the solder sled fixture with the HTS sideup.

12) Apply flux to the surface of the Take-up wire.

13) Apply flux to the HTS side of the strap.

14) Place the HTS side of the strap unto the HTS side of the take-upwire aligning the 100 mm mark with the tip of the take-up wire

15) Using the solder sled, solder the two pieces together according towork instructions.

16) After the two sections are soldered together remove wire from soldersled fixture. One overlap is complete.

17) Repeat steps 9 to 11 to solder the strap to the other wire. In thiscase the strap will be on the take-up side.

Alternate ways of making the joint include using a die that can bothsolder the wires together and form a ramp. This can replace the knifingtechnique.

Ultrasonic welding can be used in place of soldering wires to aconductive bridge. Briefly, as is known to those of skill in the art,ultrasonic welding uses high-frequency oscillations, generated by atransducer (e.g., a piezoelectric transducer) to weld metal partstogether. A sonotrode is used to induce oscillation of one workpieceagainst another, which creates a large amount of friction between theworkpieces. This friction removes impurities at the workpiece surfaces,and causes metal at the surfaces to diffuse together, forming a bondwithout causing bulk heating of the workpiece.

Cold welding can also be used in place of soldering wires to aconductive bridge. Systems and methods for cold welding metal layers areknown in the art.

Incorporation By Reference

The following documents are hereby incorporated by reference in theirentirety: U.S. Pat. No. 5,231,074, issued on Jul. 27, 1993, and entitled“Preparation of Highly Textured Oxide Superconducting Films from MODPrecursor Solutions;” U.S. Pat. No. 6,022,832, issued Feb. 8, 2000, andentitled “Low Vacuum Process for Producing Superconductor Articles withEpitaxial Layers;” U.S. Pat. No. 6,027,564, issued Feb. 22, 2000, andentitled “Low Vacuum Process for Producing Epitaxial Layers;” U.S. Pat.No. 6,190,752, issued Feb. 20, 2001, and entitled “Thin Films HavingRock-Salt-Like Structure Deposited on Amorphous Surfaces;” U.S. Pat. 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No.60/832,724, filed Jul. 21, 2006, and entitled “Low Resistance Splice forHigh Temperature Superconductor Wires;” U.S. Provisional patentapplication Ser. No. 60/832,871, filed Jul. 25, 2006, and entitled “HighTemperature Superconductors Having Planar Magnetic Flux Pinning Centersand Methods For Making The Same;” U.S. Provisional patent ApplicationSer. No. 60/866,148, filed Nov. 16, 2006, and entitled “ElectroplatedHigh-Resistivity Stabilizers In High Temperature Superconductors Andmethods Thereof;” U.S. patent application Ser. No. 11/728,108, filedMar. 23, 2007, and entitled “Systems and Methods For Solution-BasedDeposition of Metallic Cap Layers For High Temperature SuperconductorWires;” U.S. Provisional patent application Ser. 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The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in respects as illustrativeand not restrictive.

1. A laminated, spliced superconductor wire, said spliced wirecomprising: (a) a superconductor joint, comprising: (i) first and secondsuperconductor wires, each wire comprising a substrate, a superconductorlayer overlying the substrate, and a cap layer overlying thesuperconductor layer; and (ii) a conductive bridge, the conductivebridge comprising a substrate, a superconductor layer overlying thesubstrate, and a cap layer overlying the superconductor layer, whereinthe cap layer of the conductive bridge is in electrically conductivecontact with a portion of the cap layer of each of the first and secondsuperconductor wires through an electrically conductive bondingmaterial, the electrically conductive bonding material comprising lowresistance solder that forms edge seals on an end of each of the firstand second superconductor wires and on first and second ends of theconductive bridge; (b) a stabilizer structure surrounding at least aportion of the superconductor joint, wherein the superconductor joint isin electrical contact with first and second stabilizer strips; and (c) asubstantially nonporous electrically conductive filler, wherein thefiller substantially surrounds the superconductor joint.
 2. The splicedwire of claim 1, wherein the conductive bridge has a length selected toprovide the superconductor joint with a predetermined conductivity. 3.The spliced wire of claim 1, wherein the conductive bridge is bonded toat least ten millimeters of the cap layers of each of the first andsecond superconductor wires.
 4. The spliced wire of claim 1, wherein theconductive bridge is bonded to at least ten centimeters of the caplayers of each of the first and second superconductor wires.
 5. Thespliced wire of claim 1, wherein the conductive bridge comprises asection cut from one of the first and second superconductor wires. 6.The spliced wire of claim 1, wherein the filler bonds the stabilizerstructure to the superconductor joint.
 7. The spliced wire of claim 1,wherein the conductive filler comprises a material selected from thegroup consisting of solder, metal, metal alloy, metal amalgam, andconductive polymer.
 8. The spliced wire of claim 1, wherein theconductive filler and the conductive bonding material have the samecomposition.
 9. The spliced wire of claim 1, wherein the conductivefiller and the conductive bonding material have melting points thatdiffer by less than about 10%.
 10. The spliced wire of claim 1, whereinthe low resistance solder comprises one of indium, Pb—Sn, and Pb—Sn—Ag.11. The spliced wire of claim 1, wherein an end of at least one of thefirst and second superconductive wires and the conductive bridge is cutso as to mitigate stress in the spliced wire.
 12. The spliced wire ofclaim 1, wherein at least one of said ends is cut on a diagonal.
 13. Thespliced wire of claim 1, further comprising insulation surrounding atleast the superconductor joint.
 14. The spliced wire of claim 1, whereinthe first and second superconductor wires and the conductive bridge eachfurther comprise a buffer layer between the substrate and thesuperconductor layer.
 15. The spliced wire of claim 1, wherein the caplayers of the first and second superconductor wires and the cap layer ofthe conductive bridge comprise silver.
 16. The spliced wire of claim 1,wherein the stabilizer structure comprises a metal selected from thegroup consisting of aluminum, copper, silver, nickel, iron, stainlesssteel, aluminum alloy, copper alloy, silver alloy, nickel alloy, andiron alloy.
 17. The spliced wire of claim 1, wherein a conductivepathway between the first and second wires has a resistance of less thanabout 1 milli-ohm.
 18. The spliced wire of claim 1, wherein a conductivepathway between the first and second wires has a resistance of less thanabout 500 micro-ohms.
 19. The spliced wire of claim 1, wherein aconductive pathway between the first and second wires has a resistanceof less than about 200 milli-ohms.
 20. The spliced wire of claim 1,wherein a conductive pathway between the first and second wires has aresistance of less than about 100 milli-ohms.
 21. The spliced wire ofclaim 1, wherein at least one of the edge seals comprises a solder ramp.22. The spliced wire of claim 1, wherein at least one of the sealscomprises a solder bead.
 23. A laminated, spliced superconductor wire,comprising: (a) first and second stabilized superconductor wires, eachwire comprising a substrate, a superconductor layer overlying thesubstrate, a cap layer overlying the superconductor layer, andstabilizer structure bonded with electrically conductive filler to thecap layer; (b) a conductive bridge, the conductive bridge comprising asubstrate, a superconductor layer overlying the substrate, a cap layeroverlying the superconductor layer, and a stabilizer structure bondedwith electrically conductive filler to the cap layer, wherein theconductive bridge is in electrically conductive contact with a portionof each of the first and second superconductor wires through anelectrically conductive bonding material that comprises a low resistancesolder; and (c) a plurality of edge seals formed by said low resistancesolder, said plurality of edge seals including, a first edge sealsubstantially sealing an end of the first wire, a second edge sealsubstantially sealing an end of the second wire, and third and fourthedge seals respectively substantially sealing first and second ends ofthe conductive bridge.
 24. The spliced wire of claim 23, wherein thestabilizer structures of each of the first wire, second wire, andconductive bridge are thinned in regions where the conductive bridge isin electrically conductive contact with the first and second wires. 25.The spliced wire of claim 23, wherein the stabilizer structures of eachof the first wire, second wire, and conductive bridge are removed inregions where the conductive bridge is in electrically conductivecontact with the first and second wires.
 26. The spliced wire of claim23, wherein the conductive bridge is in electrically conductive contactwith at least ten millimeters of each of the first and secondsuperconductor wires.
 27. The spliced wire of claim 23, wherein theconductive bridge is in electrically conductive contact with at leastten centimeters of each of the first and second superconductor wires.28. The spliced wire of claim 23, wherein the conductive filler and theconductive bonding material have melting points that differ by less thanabout 10%.
 29. The spliced wire of claim 23, wherein a conductivepathway between the first and second wires has a resistance of less thanabout 1 milli-ohm.
 30. The spliced wire of claim 23, wherein aconductive pathway between the first and second wires has a resistanceof less than about 500 micro-ohms.
 31. The spliced wire of claim 23,wherein a conductive pathway between the first and second wires has aresistance of less than about 200 milli-ohms.
 32. The spliced wire ofclaim 23, wherein a conductive pathway between the first and secondwires has a resistance of less than about 100 milli-ohms.
 33. Thespliced wire of claim 23, wherein the stabilizer structure comprisesfirst and second stabilizer strips.
 34. The spliced wire of claim 23,wherein the electrically conductive bonding material and the conductivefiller each comprise low resistance solder.
 35. The spliced wire ofclaim 34, wherein the low resistance solder comprises one of indium,Pb—Sn, and Pb—Sn—Ag.